Two birds with one stone: SGI1 can stabilize itself and expel the IncC helper by hijacking the plasmid parABS system.

The SGI1 family integrative mobilizable elements, which are efficient agents in distribution of multidrug resistance in Gammaproteobacteria, have a complex, parasitic relationship with their IncC conjugative helper plasmids. Besides exploiting the transfer apparatus, SGI1 also hijacks IncC plasmid control mechanisms to time its own excision, replication and expression of self-encoded T4SS components, which provides advantages for SGI1 over its helpers in conjugal transfer and stable maintenance. Furthermore, SGI1 destabilizes its helpers in an unknown, replication-dependent way when they are concomitantly present in the same host. Here we report how SGI1 exploits the helper plasmid partitioning system to displace the plasmid and simultaneously increase its own stability. We show that SGI1 carries two copies of sequences mimicking the parS sites of IncC plasmids. These parS-like elements bind the ParB protein encoded by the plasmid and increase SGI1 stability by utilizing the parABS system of the plasmid for its own partitioning, through which SGI1 also destabilizes the helper plasmid. Furthermore, SGI1 expresses a small protein, Sci, which significantly strengthens this plasmid-destabilizing effect, as well as SGI1 maintenance. The plasmid-induced replication of SGI1 results in an increased copy-number of parS-like sequences and Sci expression leading to strong incompatibility with the helper plasmid.

Comparing the latent state-trait structure of the PANSS in cariprazine-medicated and placebo-controlled patients with acute schizophrenia.

After over a hundred years of research, the question whether the symptoms of schizophrenia are rather trait-like (being a relatively stable quality of individuals) or state-like (being substance to change) is still unanswered. To assess the trait and the state component in patients with acute schizophrenia, one group receiving antipsychotic treatment, the other not. Data from four phase II/III, 6-week, randomized, double-blind, placebo-controlled trials of similar design that included patients with acute exacerbation of schizophrenia were pooled. In every trial, one treatment group received a third-generation antipsychotic, cariprazine, and the other group placebo. To assess symptoms of schizophrenia, the Positive and Negative Symptom Scale (PANSS) was applied. Further analyses were conducted using the five subscales as proposed by Wallwork and colleagues. A latent state-trait (LST) model was developed to estimate the trait and state components of the total variance of the observed scores. All symptom dimensions behaved more in a trait-like manner. The proportions of all sources of variability changed over the course of the observational period, with a bent around weeks 3 and 4. Visually inspected, no major differences were found between the two treatment groups regarding the LST structure of symptom dimensions. This high proportion of inter-individual stability may represent an inherent part of symptomatology that behaves independently from treatment status.

The efficacy and safety of cariprazine in the early and late stage of schizophrenia: a post hoc analysis of three randomized, placebo-controlled trials.

BACKGROUND: The aim of the post hoc analysis was to better understand the efficacy and safety of cariprazine in patients with schizophrenia for less than 5 years (early stage) and for more than 15 years (late stage). METHODS: Data from three phase II/III randomized, double-blind, placebo-controlled trials with similar design in patients with acute exacerbation of schizophrenia were pooled and patients with early and late stage of schizophrenia were determined. A mixed-effects model for repeated measures approach was applied and least square (LS) mean changes from baseline to week 6 on the Positive and Negative Syndrome Scale (PANSS) total and factor scores were reported. Descriptive statistics were used for safety analyses including treatment emergent adverse events (TEAEs) and discontinuation rates. RESULTS: Overall, 460 patients were identified as being in the early and 414 in the late stage of schizophrenia. The pooled analysis evaluating mean change from baseline to week 6 in the PANSS total score indicated statistically significant difference between cariprazine and placebo in favor of cariprazine in both the early (LS mean difference [LSMD] -7.5 P < .001) and late stage (LSMD -6.7, P < .01) subpopulation. Early stage patients experienced similar amount of TEAEs (CAR 67.3%, PBO 54.1%) as patients in the late stage (CAR 69.6%, PBO 65.6%). CONCLUSION: In conclusion, cariprazine, a potent D3-D2 partial agonist has been found to be safe and effective in the treatment of early and late stage schizophrenia.

The investigation of the cellular electrophysiological and antiarrhythmic effects of a novel selective sodium-calcium exchanger inhibitor, GYKB-6635, in canine and guinea-pig hearts.

The sodium-calcium exchanger (NCX) is considered as the major transmembrane transport mechanism that controls Ca2+ homeostasis. Its contribution to the cardiac repolarization has not yet been directly studied due to lack of specific inhibitors, so that an urgent need for more selective compounds. In this study, the electrophysiological effects of GYKB-6635, a novel NCX inhibitor, on the NCX, L-type calcium, and main repolarizing potassium currents as well as action potential (AP) parameters were investigated. Ion currents and AP recordings were investigated by applying the whole-cell patch clamp and standard microelectrode techniques in canine heart at 37 °C. Effects of GYKB-6635 were studied in ouabain-induced arrhythmias in isolated guinea-pig hearts. At a concentration of 1 µmol/L, GYKB significantly reduced both the inward and outward NCX currents (57% and 58%, respectively). Even at a high concentration (10 µmol/L), GYKB-6635 did not change the ICaL, the maximum rate of depolarization (dV/dtmax), the main repolarizing K+ currents, and the main AP parameters. GYKB-6635 pre-treatment significantly delayed the time to the development of ventricular fibrillation (by about 18%). It is concluded that GYKB-6635 is a potent and highly selective inhibitor of the cardiac NCX and, in addition, it is suggested to also contribute to the prevention of DAD-based arrhythmias.

[Ca²âº] i-induced augmentation of the inward rectifier potassium current (IK1) in canine and human ventricular myocardium.

The inward rectifier K⁺ current (IK1) plays an important role in terminal repolarization and stabilization of the resting potential in cardiac cells. Although IK1 was shown to be sensitive to changes in intracellular Ca²âº concentration ([Ca²âº]i), the nature of this Ca²âº sensitivity-in spite of its deep influence on action potential morphology-is controversial. Therefore, we aimed to investigate the effects of a nonadrenergic rise in [Ca²âº]i on the amplitude of IK1 in canine and human ventricular myocardium and its consequences on cardiac repolarization. IK1, defined as the current inhibited by 10 µM Ba²âº, was significantly increased in isolated canine myocytes following a steady rise in [Ca²âº]i. Enhanced IK1 was also observed when [Ca²âº]i was not buffered by ethylene glycol tetraacetic acid, and [Ca²âº]I transients were generated. This [Ca²âº]i-dependent augmentation of IK1 was largely attenuated after inhibition of CaMKII by 1 µM KN-93. Elevation of [Ca²âº]o in multicellular canine and human ventricular preparations resulted in shortening of action potentials and acceleration of terminal repolarization. High [Ca²âº]o enhanced the action potential lengthening effect of the Ba(2+)-induced IK1 blockade and attenuated the prolongation of action potentials following a 0.3-µM dofetilide-induced IKr blockade. Blockade of IKs by 0.5 µM HMR-1556 had no significant effect on APD90 in either 2 mM or 4 mM [Ca²âº]o. It is concluded that high [Ca²âº]i leads to augmentation of the Ba²âº-sensitive current in dogs and humans, regardless of the mechanism of the increase. This effect seems to be at least partially mediated by a CaMKII-dependent pathway and may provide an effective endogenous defense against cardiac arrhythmias induced by Ca²âº overload.

T-tubule remodelling and ryanodine receptor organization modulate sodium-calcium exchange.

The Na(+)/Ca(2+) exchanger (NCX) is a key regulator of intracellular Ca(2+) in cardiac myocytes, predominantly contributing to Ca(2+) removal during the diastolic relaxation process but also modulating excitation-contraction coupling. NCX is preferentially located in the T-tubules and can be close to or within the dyad, where L-type Ca(2+) channels face ryanodine receptors (RyRs), the Ca(2+) release channels of the sarcoplasmic reticulum. However, especially in larger animals, not all RyRs are in dyads or adjacent to T-tubules, and a substantial fraction of Ca(2+) release from the sarcoplasmic reticulum thus occurs at distance from NCX. This chapter deals with the functional consequences of NCX location and how NCX can modulate diastolic and systolic Ca(2+) events. The loss of T-tubules and the effects on RyR function and NCX modulation are explored, as well as quantitative measurement of local Ca(2+) gradients at the level of the dyadic space.

The improvement of motor symptoms in Huntington's disease during cariprazine treatment.

BACKGROUND: Huntington's disease (HD) is a progressive neurodegenerative disease, characterised by motor disturbances and non-motor (i.e., psychiatric) symptoms. Motor symptoms are the hallmark features of HD and take many forms. Their emergence is related to alterations in striatal dopaminergic neurotransmission: dopamine levels increase in the early stages of the disease, while more advanced stages are characterised by reduced dopamine levels. Such a biphasic change potentially explains the alterations in motor symptoms: increased dopamine-production induces hyperkinetic movements early in the disease course, while depleted dopamine storage leads to hypokinetic symptoms in the advanced phase. Dopamine D2-D3 partial agonists could be a promising treatment option in HD, as they have the potential to either elevate or lower the surrounding dopamine levels if the levels are too low or too high, respectively, potentially offering symptom-relief across the illness-course. Therefore, the present study aimed at exploring the effects of cariprazine, a dopamine D2-D3 partial agonist with high affinity to D3 receptors, on motor symptoms associated with HD. METHODS: This was a single-centre, retrospective study where sixteen patients received off-label cariprazine treatment for 12 weeks (1.5-3 mg/day). Motor symptoms were evaluated using the Motor Assessment of the Unified Huntington's Disease Rating Scale. Least Square (LS) Mean Changes from Baseline (BL) to Week 8 and Week 12 in the Total Motor Score (TMS) were analysed using the Mixed Model for Repeated Measures method. In addition, improvement from BL to Week 8 and 12 was calculated for all motor items. RESULTS: Data of 16 patients were collected, but data of only 15 patients were analysed as one patient dropped out due to non-compliance. Significant changes were observed from BL to Week 8 (LS Mean Change: -9.4, p < 0.0001) and to Week 12 (LS Mean Change: -12.8, p < 0.0001) in the TMS. The improvement was captured in the majority of motor functions, excluding bradykinesia and gait. Mild akathisia was the most commonly reported side-effect, affecting 3 patients. CONCLUSION: This is the first study investigating the effectiveness of a D2-D3 partial agonist, cariprazine, in the treatment of HD. The findings of this study revealed that cariprazine was effective in the treatment of a wide range of motor symptoms associated with HD.

Data-based theoretical identification of subcellular calcium compartments and estimation of calcium dynamics in cardiac myocytes.

In cardiac cells, Ca(2+) release flux (J(rel)) via ryanodine receptors (RyRs) from the sarcoplasmic reticulum (SR) has a complex effect on the action potential (AP). Coupling between J(rel) and the AP occurs via L-type Ca(2+) channels (I(Ca)) and the Na(+)/Ca(2+) exchanger (I(NCX)). We used a combined experimental and modelling approach to study interactions between J(rel), I(Ca) and I(NCX) in porcine ventricular myocytes.We tested the hypothesis that during normal uniform J(rel), the interaction between these fluxes can be represented as occurring in two myoplasmic subcompartments for Ca(2+) distribution, one (T-space) associated with RyR and enclosed by the junctional portion of the SR membrane and corresponding T-tubular portion of the sarcolemma, the other (M-space) encompassing the rest of the myoplasm. I(Ca) and I(NCX) were partitioned into subpopulations in the T-space and M-space sarcolemma. We denoted free Ca(2+) concentrations in T-space and M-space Ca(t) and Ca(m), respectively. Experiments were designed to allow separate measurements of I(Ca) and I(NCX) as a function of J(rel). Inclusion of T-space in themodel allowed us to reproduce in silico the following important experimental results: (1) hysteresis of I(NCX) dependence on Ca(m); (2) delay between peak I(NCX) and peak Ca(m) during caffeine application protocol; (3) delay between I(NCX) and Ca(m) during Ca(2+)-induced-Ca(2+)-release; (4) rapid I(Ca) inactivation (within 2 ms) due to J(rel), with magnitude graded as a function of the SR Ca(2+) content; (5) time delay between I(Ca) inactivation due to J(rel) and Ca(m). Partition of 25% NCX in T-space and 75% in M-space provided the best fit to the experimental data. Measured Ca(m) and I(Ca) or I(NCX) were used as input to the model for estimating Ca(t). The actual model-computed Ca(t), obtained by simulating specific experimental protocols, was used as a gold standard for comparison. The model predicted peak Ca(t) in the range of 6­25 µM, with time to equilibrium of Ca(t) with Ca(m) of ~350 ms. These Ca(t) values are in the range of LCC and RyR sensitivity to Ca(2+). An increase of the SR Ca(2+) load increased the time to equilibrium. The I(Ca)-based estimation method was most accurate during the ascending phase of Ca(t). The I(NCX)-based method provided a good estimate for the descending phase of Ca(t). Thus, application of both methods in combination provides the best estimate of the entire Ca(t) time course.

Depressive Symptoms and PANSS Symptom Dimensions in Patients With Predominant Negative Symptom Schizophrenia: A Network Analysis.

Introduction: Schizophrenia is a severe psychiatric disorder with a large symptomatic heterogeneity. Moreover, many patients with schizophrenia present with comorbid psychiatric symptoms or disorders. The relation between depressive symptoms and negative symptoms, such as blunted affect, alogia, anhedonia, asociality and avolition, is particularly intriguing. The negative symptoms can be primary or secondary of depression or overlapping with depressive symptoms. The aim of the present network analysis was to better understand the interactions between depressive symptoms and the different symptoms of schizophrenia and to investigate whether negative symptoms and depressive symptoms can be better delineated. Methods: A network analysis on the baseline item scores of the Positive and Negative Syndrome Scale (PANSS) and Calgary Depression Scale for Schizophrenia (CDSS) from the cariprazine-risperidone study in patients with predominant negative symptoms (PNS) was performed. The connections between all these symptoms (PANSS and CDSS) were investiged: node strength and network centrality were estimated and the Mohr 5-factor model of the PANSS was applied to test the validity of its different symptoms clusters. Results: Across 460 patients with schizophrenia and PNS, the most central symptom (largest node strength) was depression (PANSS) followed by depression (CDSS), anxiety, lack of judgment and insight and tension. The PANSS negative symptom cluster together and was only poorly connected with CDSS depresson symptoms. The Mohr 5 factor model was clearly recognized in the overall clustering of symptoms. Conclusion: This network analysis suggests that depression and anxiety symptoms are the most central in this PNS patient population, despite the baseline low depression scores, and that negative symptoms are a clearly independent symptom cluster that can be delineated from depressive symptoms.

What Is the Minimum Clinically Important Change in Negative Symptoms of Schizophrenia? PANSS Based Post-hoc Analyses of a Phase III Clinical Trial.

Introduction: Minimum clinically important difference (MCID) is a measure that defines the minimum amount of change in an objective score of a clinical test that must be reached for that change to be clinically noticeable. We aimed to find the MCID for patients with predominantly negative symptoms of schizophrenia at its earliest occurrence. Methods: Data of a 26-week long, double-blind study with 454 patients [Positive and Negative Symptom Scale Negative Factor Score (PANSS-FSNS) ≥24, Positive and Negative Symptom Scale Positive Factor Score (PANSS-FSPS) ≤ 19] treated with cariprazine 4.5 mg/d or risperidone 4 mg/d were analyzed. The Clinical Global Impression-Improvement scale was used to quantify minimum improvement (CGI-I = 3) and no clinical change (CGI-I = 4) on the PANSS-FSNS, and the MCID was estimated with the following methods: as the mean PANSS-FSNS changes corresponding to the first instance of minimal improvement across all visits (MCID1); as the difference between the PANSS-FSNS change associated with the first instance and the PANSS-FSNS changes associated with the last recorded clinically unchanged status across all visits (MCID2); with the effect size approach (MCID3); as the Youden Index based cut-off value between no clinical change and minimal improvement (MCID4); as the relative likelihood of minimal improvement (MCID5). Results: The MCID1 and MCID2 resulted in, respectively, a 3.8-point (18.5%) and a 1.5-point (7.3%) decrease from baseline severity on the PANSS-FSNS. Greater values were required for the MCID at later evaluation times. The cut-off between minimum improvement and no clinical change defined by the Youden Index was a-3-point (15%) change in the PANSS-FSNS. The effect size approach indicated the 1.5-point difference between minimally improved and unchanged patients to be a medium effect (ES = 0.6). Conclusion: Applying different methods led to different results, ranging between 7.3 and 18.5% improvement from the baseline for the MCID at its earliest occurrence in patients with predominantly negative symptoms of schizophrenia.

Microdomain [Ca²âº] near ryanodine receptors as reported by L-type Ca²âº and Na+/Ca²âº exchange currents.

During Ca²âº release from the sarcoplasmic reticulum triggered by Ca²âº influx through L-type Ca²âº channels (LTCCs), [Ca²âº] near release sites ([Ca²âº]nrs) temporarily exceeds global cytosolic [Ca²âº]. [Ca²âº]nrs can at present not be measured directly but the Na+/Ca2+ exchanger (NCX) near release sites and LTCCs also experience [Ca²âº]nrs. We have tested the hypothesis that ICaL and INCX could be calibrated to report [Ca²âº]nrs and would report different time course and values for local [Ca²âº]. Experiments were performed in pig ventricular myocytes (whole-cell voltage-clamp, Fluo-3 to monitor global cytosolic [Ca²âº], 37◦C). [Ca²âº]nrs-dependent inactivation of ICaL during a step to +10 mV peaked around 10 ms. For INCX we computationally isolateda current fraction activated by [Ca²âº]nrs; values were maximal at 10 ms into depolarization. The recovery of [Ca²âº]nrs was comparable with both reporters (>90% within 50 ms). Calibration yielded maximal values for [Ca²âº]nrs between 10 and 15 µmol l⁻¹ with both methods. When applied to a step to less positive potentials (-30 to -20 mV), the time course of [Ca²âº]nrs was slower but peak values were not very different. In conclusion, both ICaL inactivation and INCX activation, using a subcomponent analysis, can be used to report dynamic changes of [Ca²âº]nrs. Absolute values obtained by these different methods are within the same range, suggesting that they are reporting on a similar functional compartment near ryanodine receptors. Comparable [Ca²âº]nrs at +10 mV and -20 mV suggests that, although the number of activated release sites differs at these potentials, local gradients at release sites can reach similar values.

Safety and Tolerability of Cariprazine in Patients with Schizophrenia: A Pooled Analysis of Eight Phase II/III Studies.

BACKGROUND: Long-term treatment with antipsychotic agents is indicated for patients with schizophrenia, but treatment is associated with adverse events (AEs) that contribute to medication discontinuation and nonadherence. Understanding drug safety profiles is critical to avoid unwanted side effects. Cariprazine is a potent dopamine D3/D2 receptor partial agonist that is approved for the treatment of adults with schizophrenia (EU, US) and acute manic/mixed and depressive episodes associated with bipolar I disorder (US). METHODS: Post hoc analyses were conducted to characterize the safety profile of cariprazine within the recommended 1.5-6 mg/d dose range for schizophrenia; data from 8 short- or long-term clinical trials were analyzed. RESULTS: In the pooled cariprazine-treated safety population (n=2048), the rate of study completion was 52.8%, with withdrawal of consent, insufficient response, and AEs the most common reasons for premature discontinuation. The most commonly reported AEs (>10%) in the overall cariprazine-treatment group were akathisia (14.6%), insomnia (14.0%), and headache (12.1%); most AEs were considered mild (71.0%) or moderate (26.5%). Most akathisia was mild/moderate (97.5%) and >93% of patients remained on treatment; akathisia events were managed by rescue medications (56.3%) or dose reduction (18.3%). The metabolic profile of cariprazine was neutral in patients with short- and long-term exposure; mean weight gain was 1 kg for overall cariprazine, with an AE of weight increased reported for 5.1%. Other AEs of special interest that occurred at >3% for overall cariprazine were extrapyramidal disorder (7.0%), sedation (3.7%), and somnolence (3.1%); prolactin elevation, cognition impairment, sexual dysfunction, suicidality, and QT prolongation occurred at ≤1%. CONCLUSION: Akathisia, the most common cariprazine-related AE, was mild/moderate and resulted in few study discontinuations; symptoms were well managed and most patients remained on treatment. Results of this analysis indicated that cariprazine in the recommended dose range was safe and generally well tolerated in patients with schizophrenia. TRIAL REGISTRATION: Studies registered with ClinicalTrials.gov (NCT00404573, NCT01104779, NCT00694707, NCT01104766, NCT01104792, NCT00839852, and NCT01412060) and EudraCT (2012-005485-36).

Improving Mood and Cognitive Symptoms in Huntington's Disease With Cariprazine Treatment.

In Huntington's disease (HD), the main clinical symptoms include depression, apathy, cognitive deficits, motor deficiencies and involuntary movements. Cognitive, mood and behavioral changes may precede motor symptoms by up to 15 years. The treatment of these diverse symptoms is challenging. Tetrabenazine and deutetrabenazine are the only medications specifically approved for Huntington's chorea, but they do not affect the non-motor symptoms. For these, antidepressants, antipsychotics, and benzodiazepines have demonstrated benefit in some cases and can be used off-label. These drugs, due to sedative side effects, may negatively influence cognition. Sixteen patients having HD received a 12-week off-label cariprazine (CAR) treatment (1.5-3 mg/day). Cognitive performance and behavioral changes were measured by the Addenbrooke Cognitive Examination (ACE) test, the Cognitive and Behavioral part of the Unified Huntington's Disease Rating Scale (UHDRS), and the Beck Depression Inventory (BDI). Mixed model for repeated measures was fitted to the data, with terms of visit, baseline (BL) and their interaction. Cariprazine treatment resulted in the following changes from BL to week 12, respectively: the mean score of BDI decreased from 17.7 ± 10.7 to 10.0 ± 10.7 (p <0.0097), while the Behavioral Assessment score of the UHDRS decreased from 54.9 ± 11.3 to 32.5 ± 15.4 (p < 0.0001); ACE score increased from 75.1 ± 11.0 to 89.0 ± 9.3 (p < 0.0001); Cognitive Verbal Fluency score from 6.2 ± 2.5 to 7.7 ± 2.7 (p < 0.0103); Symbol Digit Test from 9.2 ± 6.9 to 12.3 ± 8.9 (p < 0.0009). Mild akathisia was the most frequent side effect, presenting in 2 out of 16 patients (12.5%). We conclude that CAR had a positive effect on depressive mood, apathy and cognitive functions in patients with early stage of HD. Based on the neurobiological basis of these symptoms, CAR can improve the dopamine imbalance of the prefrontal cortex. This draws attention to the transdiagnostic approach which supports the further understanding of the similar symptomatology of different neuropsychiatric disorders and helps to identify new indications of pharmaceutical compounds.

Disentangling the symptoms of schizophrenia: Network analysis in acute phase patients and in patients with predominant negative symptoms.

BACKGROUND: The Positive and Negative Syndrome Scale (PANSS) is widely used in schizophrenia and has been divided into distinct factors (5-factor models) and subfactors. Network analyses are newer in psychiatry and can help to better understand the relationships and interactions between the symptoms of a psychiatric disorder. The aim of this study was threefold: (a) to evaluate connections between schizophrenia symptoms in two populations of patients (patients in the acutely exacerbated phase of schizophrenia and patients with predominant negative symptoms [PNS]), (b) to test whether network analyses support the Mohr 5 factor model of the PANSS and the Kahn 2 factor model of negative symptoms, and finally (c) to identify the most central symptoms in the two populations. METHODS: Using pooled baseline data from four cariprazine clinical trials in patients with acute exacerbation of schizophrenia (n = 2193) and the cariprazine-risperidone study in patients with PNS (n = 460), separate network analyses were performed. Network structures were estimated for all 30 items of the PANSS. RESULTS: While negative symptoms in patients with an acute exacerbation of schizophrenia are correlated with other PANSS symptoms, these negative symptoms are not correlated with other PANSS symptoms in patients with PNS. The Mohr factors were partially reflected in the network analyses. The two most central symptoms (largest node strength) were delusions and uncooperativeness in acute phase patients and hostility and delusions in patients with PNS. CONCLUSIONS: This network analysis suggests that symptoms of schizophrenia are differently structured in acute and PNS patients. While in the former, negative symptoms are mainly secondary, in patients with PNS, they are mainly primary. Further, primary negative symptoms are better conceptualized as distinct negative symptom dimensions of the PANSS.

Cellular contribution to left and right atrial dysfunction in chronic arterial hypertension in pigs.

AIMS: Atrial contractile dysfunction contributes to worse prognosis in hypertensive heart disease (HHD), but the role of cardiomyocyte dysfunction in atrial remodelling in HHD is not well understood. We investigated and compared cellular mechanisms of left (LA) and right atrial (RA) contractile dysfunction in pigs with HHD. METHODS AND RESULTS: In vivo electrophysiological and magnetic resonance imaging studies were performed in control and pigs treated with 11-deoxycorticosterone acetate (DOCA)/high-salt/glucose diet (12 weeks) to induce HHD. HHD leads to significant atrial remodelling and loss of contractile function in LA and a similar trend in RA (magnetic resonance imaging). Atrial remodelling was associated with a higher inducibility of atrial fibrillation but unrelated to changes in atrial refractory period or fibrosis (histology). Reduced atrial function in DOCA pigs was related to reduced contraction amplitude of isolated LA (already at baseline) and RA myocytes (at higher frequencies) due to reduced intracellular Ca release (Fura 2-AM, field stimulation). However, Ca regulation differed in LA and RA cardiomyocytes: LA cardiomyocytes showed reduced sarcoplasmic reticulum (SR) [Ca], whereas in RA, SR [Ca] was unchanged and SR Ca2+ -ATPase activity was increased. Sodium-calcium exchanger (NCX) activity was not significantly altered. We used ORM-10103 (3 µM), a specific NCX inhibitor to improve Ca availability in LA and RA cardiomyocytes from DOCA pigs. Partial inhibition of NCX increased Ca2+ transient amplitude and SR Ca in LA, but not RA cells. CONCLUSIONS: In this large animal model of HHD, atrial remodelling in sinus rhythm in vivo was related to differential LA and RA cardiomyocyte dysfunction and Ca signalling. Selective acute inhibition of NCX improved Ca release in diseased LA cardiomyocytes, suggesting a potential therapeutic approach to improve atrial inotropy in HHD.

Increased Ca2+ content of the sarcoplasmic reticulum provides arrhythmogenic trigger source in swimming-induced rat athlete's heart model.

Sudden cardiac death among top athletes is very rare, however, it is 2-4 times more frequent than in the age-matched control population. In the present study, the electrophysiological consequences of long-term exercise training were investigated on Ca2+ homeostasis and ventricular repolarization, together with the underlying alterations of ion channel expression, in a rat athlete's heart model. 12-week swimming exercise-trained and control Wistar rats were used. Electrophysiological data were obtained by using ECG, patch clamp and fluorescent optical measurements. Protein and mRNA levels were determined by the Western immunoblot and qRT-PCR techniques. Animals in the trained group exhibited significantly lower resting heart rate, higher incidence of extrasystoles and spontaneous Ca2+ release events. The Ca2+ content of the sarcoplasmic reticulum (SR) and the Ca2+ transient amplitude were significantly larger in the trained group. Intensive physical training is associated with elevated SR Ca2+ content, which could be an important part of physiological cardiac adaptation mechanism to training. However, it may also sensitize the heart for the development of spontaneous Ca2+ release and extrasystoles. Training-associated remodeling may promote elevated incidence of life threatening arrhythmias in top athletes.

Does small-conductance calcium-activated potassium channel contribute to cardiac repolarization?

Small-conductance calcium-activated potassium channels (SK channels) have a significant role in neurons. Since they directly integrate calcium handling with repolarization, in heart their role would be particularly important. However, their contribution to cardiac repolarization is still unclear. A previous study reported a significant lengthening effect of apamin, a selective SK channel inhibitor, on the action potential duration in atrial and ventricular mouse cardiomyocytes and human atrial cells. They concluded that these channels provide an important functional link between intracellular calcium handling and action potential kinetics. These findings seriously contradict our studies on cardiac "repolarization reserve", where we demonstrated that inhibition of a potassium current is not likely to cause excessive APD lengthening, since its decrease is mostly compensated by a secondary increase in other, unblocked potassium currents. To clarify this contradiction, we reinvestigated the role of the SK current in cardiac repolarization, using conventional microelectrode and voltage-clamp techniques in rat and dog atrial and ventricular multicellular preparations, and in isolated cardiomyocytes. SK2 channel expression was confirmed with immunoblot technique and confocal microscopy. We found, that while SK2 channels are expressed in the myocardium, a full blockade of these channels by 100 nM apamin--in contrast to the previous report--did not cause measurable electrophysiological changes in mammalian myocardium, even when the repolarization reserve was blunted. These results clearly demonstrate that in rat, dog and human ventricular cells under normal physiological conditions--though present--SK2 channels are not active and do not contribute to action potential repolarization.

Contribution of I Kr and I K1 to ventricular repolarization in canine and human myocytes: is there any influence of action potential duration?

BACKGROUND: The aim of the present work was to study the profile of the rapid delayed rectifier potassium current (I (Kr)) and the inward rectifier potassium current (I (K1)) during ventricular repolarization as a function of action potential duration and rate of repolarization. METHODS: Whole cell configuration of the patch clamp technique was used to monitor I (Kr) and I (K1) during the action potential plateau and terminal repolarization. Action potentials recorded at various cycle lengths (0.4-5 s) and repolarizing voltage ramps having various slopes (0.5-3 V/s) were used as command signals. I (Kr) and I (K1) were identified as difference currents dissected by E-4031 and BaCl(2), respectively. RESULTS: Neither peak amplitudes nor mean values of I (Kr) and I (K1) recorded during the plateau of canine action potentials were influenced by action potential duration. The membrane potential where I (Kr) and I (K1) peaked during the terminal repolarization was also independent of action potential duration. Similar results were obtained in undiseased human ventricular myocytes, and also in canine cells when I (Kr) and I (K1) were evoked using repolarizing voltage ramps of various slopes. Action potential voltage clamp experiments revealed that the peak values of I (Kr), I (K1), and net outward current during the terminal repolarization were independent of the pacing cycle length within the range of 0.4 and 5 s. CONCLUSIONS: The results indicate that action potential configuration fails to influence the amplitude of I (Kr) and I (K1) during the ventricular action potential in dogs and humans, suggesting that rate-dependent changes in action potential duration are not likely related to rate-dependent alterations in I (Kr) or I (K1) kinetics in these species.

The Na+/Ca2+ exchange blocker SEA0400 fails to enhance cytosolic Ca2+ transient and contractility in canine ventricular cardiomyocytes.

AIMS: This study was designed to evaluate the effects of the Na(+)/Ca(2+) exchange (NCX) inhibitor SEA0400 on Ca(2+) handling in isolated canine ventricular myocytes. METHODS AND RESULTS: Intracellular Ca(2+) ([Ca(2+)](i)) transients, induced by either field stimulation or caffeine flush, were monitored using Ca(2+) indicator dyes. [Ca(2+)](i)-dependent modulation of the inhibitory effect of SEA0400 on NCX was characterized by the changes in Ni(2+)-sensitive current in voltage-clamped myocytes. Sarcoplasmic reticulum (SR) Ca(2+) release and uptake were studied in SR membrane vesicles. Gating properties of single-ryanodine receptors were analysed in lipid bilayers. Ca(2+) sensitivity of the contractile machinery was evaluated in chemically skinned myocytes. In myocytes paced at 1 Hz, neither diastolic [Ca(2+)](i) nor the amplitude of [Ca(2+)](i) transients was significantly altered by SEA0400 up to the concentration of 1 microM, which was shown to inhibit the exchange current. The blocking effect of SEA0400 on NCX decreased with increasing [Ca(2+)](i), and it was more pronounced in reverse than in forward mode operation at every [Ca(2+)](i) examined. The rate of decay of the caffeine-induced [Ca(2+)](i) transients was decreased significantly by 1 microM SEA0400; however, this effect was only a fraction of that observed with 10 mM NiCl(2). Neither SR Ca(2+) release and uptake nor cell shortening and Ca(2+) sensitivity of the contractile proteins were influenced by SEA0400. CONCLUSION: The lack of any major SEA0400-induced shift in Ca(2+) transients or contractility of myocytes can well be explained by its limited inhibitory effect on NCX (further attenuated by elevated [Ca(2+)](i) levels) and a concomitant reduction in Ca(2+) influx due to the predominantly reverse mode blockade of NCX and suppression of L-type Ca(2+) current.

Linking PANSS negative symptom scores with the Clinical Global Impressions Scale: understanding negative symptom scores in schizophrenia.

Understanding how rating scale improvement corresponds to a clinical impression in patients with negative symptoms of schizophrenia may help define the clinical relevance of change in this patient population. We conducted post hoc equipercentile linking analyses of Positive and Negative Syndrome Scale (PANSS) outcomes (e.g., PANSS-Factor Score for Negative Symptoms [FSNS]) with Clinical Global Impressions-Improvement (CGI-I) and -Severity (CGI-S) ratings on data from patients treated with cariprazine (n = 227) or risperidone (n = 229) in a clinical study evaluating negative symptoms in schizophrenia. Patients were prospectively selected for persistent, predominant negative symptoms of schizophrenia (PNS), and minimal positive/depressive/extrapyramidal symptoms. Linking results demonstrated that greater improvement on PANSS-derived measures corresponded to clinical impressions of greater improvement, as measured by the CGI-I, and less severe disease states, as measured by the CGI-S. For example, CGI-S scores of 1 (normal), 2, 3, 4, 5, and 6 (severely ill) corresponded to PANSS-FSNS scores of 7, 13, 19, 24, 29, and 35, respectively. Likewise, CGI-I scores of minimally improved, much improved, and very much improved corresponded to a change from baseline in PANSS-FSNS scores of -27%, -49%, and -100%, respectively. These are important findings for the interpretation of the results of trials in patients with persistent negative symptoms.