"Local control": another core concept of physiology.

The maintenance of a more or less constant internal environment by homeostatic (negative feedback) mechanisms is well understood, and "homeostasis" is regarded as an important core concept for students to understand. However, there are critically important control mechanisms that operate at the local level and are more or less independent of homeostasis. Here we define a core concept of "local control," present examples of it in many different organ systems, and propose a conceptual framework for it. Local control, like all of the other core concepts, can provide students with a learning tool that can facilitate understanding physiology.NEW & NOTEWORTHY Local control of many physiological phenomena occurs to meet the needs of certain systems and to enable these systems to meet the episodic challenges that occur. The mechanisms by which local control is exerted include locally released chemical messengers, physical stimuli acting on the structures, and local neural networks. Examples of important local controls are present throughout the body.

Non-Invasive Assessment of Back Surface Topography: Technologies, Techniques and Clinical Utility.

(1) Background: Frequent exposure to ionising radiation is often used to determine the diagnosis of adolescent idiopathic scoliosis (AIS), a lateral curvature of the spine in those aged between 10 and 18 years, and a treatment plan according to Cobb angle. This narrative review outlines the clinical utility of surface topography (ST), a radiation-free imaging modality. (2) Methods: Publicly available databases were searched to yield literature related to ST. Identified articles were classified based on the equipment used and in order of how it was developed, i.e., historical, recent developments, and state-of-the-art developments. (3) Conclusions: ST is a reliable cost-effective non-invasive technique that provides an alternative to radiation-based imaging to aid with the diagnosis and potential screening of AIS. Several scanning methods are available, which allows ST to be used in several clinical environments. Limitations of inter-reliability and differences of apparatus resulting in variations of data have been noted through this narrative review.

Sarcoplasmic reticulum Ca2+, Mg2+, K+, and Cl- concentrations adjust quickly as heart rate changes.

During systole, Ca2+ is released from the sarcoplasmic reticulum (SR) through ryanodine receptors (RyRs) while, simultaneously, other ions (specifically K+, Mg2+, and Cl-) provide counter-ion flux. These ions move back into the SR during diastole through the SERCA pump and SR K+ and Cl- channels. In homeostasis, all ion concentrations in different cellular regions (e.g., junctional and non-junctional SR, dyadic cleft, and cytosol) are the same at the beginning and end of the cardiac cycle. Here, we used an equivalent circuit compartment model of the SR and the surrounding cytoplasm to understand the heart rate dependence of SR ion homeostasis. We found that the Ca2+, Mg2+, K+, and Cl- concentrations in the SR and the cytoplasm self-adjust within just a few heartbeats with only very small changes in Mg2+, K+, and Cl- concentrations and membrane voltages (just a few percent). However, those small changes were enough to compensate for the large heart-rate-dependent changes in SR and cytoplasmic Ca2+ concentrations in the new steady state. The modeling suggests that ion adaptation to increases in heart rate is inherent to the system and that physiological changes that increase contractility and cardiac output are accommodated by the same self-adjusting mechanism of producing small changes in ion driving forces. Our findings also support the long-held hypothesis that SR membrane potentials are small (~1-2mV).

ß-Adrenergic induced SR Ca2+ leak is mediated by an Epac-NOS pathway.

Cardiac ß-adrenergic receptors (ß-AR) and Ca2+-Calmodulin dependent protein kinase (CaMKII) regulate both physiological and pathophysiological Ca2+ signaling. Elevated diastolic Ca2+ leak from the sarcoplasmic reticulum (SR) contributes to contractile dysfunction in heart failure and to arrhythmogenesis. ß-AR activation is known to increase SR Ca2+ leak via CaMKII-dependent phosphorylation of the ryanodine receptor. Two independent and reportedly parallel pathways have been implicated in this ß-AR-CaMKII cascade, one involving exchange protein directly activated by cAMP (Epac2) and another involving nitric oxide synthase 1 (NOS1). Here we tested whether Epac and NOS function in a single series pathway to increase ß-AR induced and CaMKII-dependent SR Ca2+ leak. Leak was measured as both Ca2+ spark frequency and tetracaine-induced shifts in SR Ca2+, in mouse and rabbit ventricular myocytes. Direct Epac activation by 8-CPT (8-(4-chlorophenylthio)-2'-O-methyl-cAMP) mimicked ß-AR-induced SR Ca2+ leak, and both were blocked by NOS inhibition. The same was true for myocyte CaMKII activation (assessed via a FRET-based reporter) and ryanodine receptor phosphorylation. Inhibitor and phosphorylation studies also implicated phosphoinositide 3-kinase (PI3K) and protein kinase B (Akt) downstream of Epac and above NOS activation in this pathway. We conclude that these two independently characterized parallel pathways function mainly via a single series arrangement (ß-AR-cAMP-Epac-PI3K-Akt-NOS1-CaMKII) to mediate increased SR Ca2+ leak. Thus, for ß-AR activation the cAMP-PKA branch effects inotropy and lusitropy (by effects on Ca2+ current and SR Ca2+-ATPase), this cAMP-Epac-NOS pathway increases pathological diastolic SR Ca2+leak. This pathway distinction may allow novel SR Ca2+ leak therapeutic targeting in treatment of arrhythmias in heart failure that spare the inotropic and lusitropic effects of the PKA branch.

Sarcoplasmic Reticulum Structure and Functional Properties that Promote Long-Lasting Calcium Sparks.

Calcium (Ca) sparks are the fundamental sarcoplasmic reticulum (SR) Ca release events in cardiac myocytes, and they have a typical duration of 20-40 ms. However, when a fraction of ryanodine receptors (RyRs) are blocked by tetracaine or ruthenium red, Ca sparks lasting hundreds of milliseconds have been observed experimentally. The fundamental mechanism underlying these extremely prolonged Ca sparks is not understood. In this study, we use a physiologically detailed mathematical model of subcellular Ca cycling to examine how Ca spark duration is influenced by the number of functional RyRs in a junctional cluster (which is reduced by tetracaine or ruthenium red) and other SR Ca handling properties. One RyR cluster contains a few to several hundred RyRs, and we use a four-state Markov RyR gating model. Each RyR opens stochastically and is regulated by cytosolic and luminal Ca. We varied the number of functional RyRs in the single cluster, diffusion within the SR network, diffusion between network and junctional SR, cytosolic Ca diffusion, SERCA uptake activity, and RyR open probability. For long-lasting Ca release events, opening events within the cluster must occur continuously because the typical open time of the RyR is only a few milliseconds. We found the following: 1) if the number of RyRs is too small, it is difficult to maintain consecutive openings and stochastic attrition terminates the release; 2) if the number of RyRs is too large, the depletion of Ca from the junctional SR terminates the release; and 3) very long release events require relatively small-sized RyR clusters (reducing flux as seen experimentally with tetracaine) and sufficiently rapid intra-SR Ca diffusion, such that local junctional intra-SR [Ca] can be maintained by intra-SR diffusion and overall SR Ca reuptake.

Electrophysiological Determination of Submembrane Na(+) Concentration in Cardiac Myocytes.

In the heart, Na(+) is a key modulator of the action potential, Ca(2+) homeostasis, energetics, and contractility. Because Na(+) currents and cotransport fluxes depend on the Na(+) concentration in the submembrane region, it is necessary to accurately estimate the submembrane Na(+) concentration ([Na(+)]sm). Current methods using Na(+)-sensitive fluorescent indicators or Na(+) -sensitive electrodes cannot measure [Na(+)]sm. However, electrophysiology methods are ideal for measuring [Na(+)]sm. In this article, we develop patch-clamp protocols and experimental conditions to determine the upper bound of [Na(+)]sm at the peak of action potential and its lower bound at the resting state. During the cardiac cycle, the value of [Na(+)]sm is constrained within these bounds. We conducted experiments in rabbit ventricular myocytes at body temperature and found that 1) at a low pacing frequency of 0.5 Hz, the upper and lower bounds converge at 9 mM, constraining the [Na(+)]sm value to ∼9 mM; 2) at 2 Hz pacing frequency, [Na(+)]sm is bounded between 9 mM at resting state and 11.5 mM; and 3) the cells can maintain [Na(+)]sm to the above values, despite changes in the pipette Na(+) concentration, showing autoregulation of Na(+) in beating cardiomyocytes.

Isoproterenol increases the fraction of spark-dependent RyR-mediated leak in ventricular myocytes.

Recent research suggests that the diastolic ryanodine-receptor-mediated release of Ca(2+) (J(leak)) from the sarcoplasmic reticulum of ventricular myocytes occurs in spark and nonspark forms. Further information about the role(s) of these release manifestations is scarce, however. This study addresses whether the fraction of spark-mediated J(leak) increases due to ß-adrenergic stimulation. Confocal microscopy was used to simultaneously image Ca(2+) sparks and quantify J(leak) in intact rabbit myocytes, either in the absence or in the presence of 125 nM isoproterenol. It was found that isoproterenol treatment shifts the spark-frequency-J(leak) relationship toward an increased sensitivity to a [Ca(2+)] trigger. In agreement, a small but significant increase in spark width was found for cells with matched baseline [Ca(2+)] and total SR [Ca(2+)]. The reconstruction of release fluxes, when applied to the average sparks from those selected cells, yielded a wider release source in the isoproterenol event, indicating the recruitment of peripheral ryanodine receptors. Overall, the results presented here indicate that ß-adrenergic stimulation increases the spark-dependent fraction of J(leak). Working together, the increased Ca(2+) sensitivity and the greater spark width found during isoproterenol treatment may increase the probability of Ca(2+) wave generation.

Sarcoplasmic reticulum K(+) (TRIC) channel does not carry essential countercurrent during Ca(2+) release.

The charge translocation associated with sarcoplasmic reticulum (SR) Ca(2+) efflux is compensated for by a simultaneous SR K(+) influx. This influx is essential because, with no countercurrent, the SR membrane potential (Vm) would quickly (<1 ms) reach the Ca(2+) equilibrium potential and SR Ca(2+) release would cease. The SR K(+) trimeric intracellular cation (TRIC) channel has been proposed to carry the essential countercurrent. However, the ryanodine receptor (RyR) itself also carries a substantial K(+) countercurrent during release. To better define the physiological role of the SR K(+) channel, we compared SR Ca(2+) transport in saponin-permeabilized cardiomyocytes before and after limiting SR K(+) channel function. Specifically, we reduced SR K(+) channel conduction 35 and 88% by replacing cytosolic K(+) for Na(+) or Cs(+) (respectively), changes that have little effect on RyR function. Calcium sparks, SR Ca(2+) reloading, and caffeine-evoked Ca(2+) release amplitude (and rate) were unaffected by these ionic changes. Our results show that countercurrent carried by SR K(+) (TRIC) channels is not required to support SR Ca(2+) release (or uptake). Because K(+) enters the SR through RyRs during release, the SR K(+) (TRIC) channel most likely is needed to restore trans-SR K(+) balance after RyRs close, assuring SR Vm stays near 0 mV.

Calcium movements inside the sarcoplasmic reticulum of cardiac myocytes.

Sarcoplasmic reticulum (SR) Ca content ([Ca]SRT) is critical to both normal cardiac function and electrophysiology, and changes associated with pathology contribute to systolic and diastolic dysfunction and arrhythmias. The intra-SR free [Ca] ([Ca]SR) dictates the [Ca]SRT, the driving force for Ca release and regulates release channel gating. We discuss measurement of [Ca]SR and [Ca]SRT, how [Ca]SR regulates activation and termination of release, and how Ca diffuses within the SR and influences SR Ca release during excitation-contraction coupling, Ca sparks and Cac waves. The entire SR network is connected and its lumen is also continuous with the nuclear envelope. Rapid Ca diffusion within the SR could stabilize and balance local [Ca]SR within the myocyte, but restrictions to diffusion can create spatial inhomogeneities. Experimental measurements and mathematical models of [Ca]SR to date have greatly enriched our understanding of these [Ca]SR dynamics, but controversies exist and may stimulate new measurements and analysis.

Dynamic calcium movement inside cardiac sarcoplasmic reticulum during release.

RATIONALE: Intra-sarcoplasmic reticulum (SR) free [Ca] ([Ca](SR)) provides the driving force for SR Ca release and is a key regulator of SR Ca release channel gating during normal SR Ca release or arrhythmogenic spontaneous Ca release events. However, little is known about [Ca](SR) spatiotemporal dynamics. OBJECTIVE: To directly measure local [Ca](SR) with subsarcomeric spatiotemporal resolution during both normal global SR Ca release and spontaneous Ca sparks and to evaluate the quantitative implications of spatial [Ca](SR) gradients. METHODS AND RESULTS: Intact and permeabilized rabbit ventricular myocytes were subjected to direct simultaneous measurement of cytosolic [Ca] and [Ca](SR) and FRAP (fluorescence recovery after photobleach). We found no detectable [Ca](SR) gradients between SR release sites (junctional SR) and Ca uptake sites (free SR) during normal global Ca release, clear spatiotemporal [Ca](SR) gradients during isolated Ca blinks, faster intra-SR diffusion in the longitudinal versus transverse direction, 3- to 4-fold slower diffusion of fluorophores in the SR than in cytosol, and that intra-SR Ca diffusion varies locally, dependent on local SR connectivity. A computational model clarified why spatiotemporal gradients are more detectable in isolated local releases versus global releases and provides a quantitative framework for understanding intra-SR Ca diffusion. CONCLUSIONS: Intra-SR Ca diffusion is rapid, limiting spatial [Ca](SR) gradients during excitation-contraction coupling. Spatiotemporal [Ca](SR) gradients are apparent during Ca sparks, and these observations constrain models of dynamic Ca movement inside the SR. This has important implications for myocyte SR Ca handling, synchrony, and potentially arrhythmogenic spontaneous contraction.

Longitudinal and transversal propagation of excitation along the tubular system of rat fast-twitch muscle fibres studied by high speed confocal microscopy.

Mammalian skeletal muscle fibres possess a tubular (t-) system that consists of regularly spaced transverse elements which are also connected in the longitudinal direction. This tubular network provides a pathway for the propagation of action potentials (APs) both radially and longitudinally within the fibre, but little is known about the actual radial and longitudinal AP conduction velocities along the tubular network in mammalian skeletal muscle fibres. The aim of this study was to track AP propagation within the t-system network of fast-twitch rat muscle fibres with high spatio-temporal resolution when the t-system was isolated from the surface membrane. For this we used high speed confocal imaging of AP-induced Ca(2+) release in contraction-suppressed mechanically skinned fast-twitch fibres where the t-system can be electrically excited in the absence of the surface membrane. Supramaximal field pulses normally elicited a synchronous AP-induced release of Ca(2+) along one side of the fibre axis which propagated uniformly across the fibre. In some cases up to 80 or more adjacent transverse tubules failed to be excited by the field pulse, while adjacent areas responded with normal Ca(2+) release. In these cases a continuous front of Ca(2+) release with an angle to the scanning line was observed due to APs propagating longitudinally. From these observations the radial/transversal and longitudinal AP conduction velocities along the tubular network deeper in the fibre under our conditions (19 ± 1°C) ranged between 8 and 11 µm ms(-1) and 5 to 9 µm ms(-1), respectively, using different methods of estimation. The longitudinal propagation of APs appeared to be markedly faster closer to the edge of the fibre, in agreement with the presence of dense longitudinal connections immediately below the surface of the fibre and more sparse connections at deeper planes within the fibre. During long trains of closely spaced field pulses the AP-elicited Ca(2+) releases became non-synchronous along the fibre axis. This is most likely caused by local tubular K(+) accumulation that produces local depolarization and local slowing of AP propagation. Longitudinally propagating APs may reduce such inhomogeneities by exciting areas of delayed AP onset. Clearly, the longitudinal tubular pathways within the fibre for excitation are used as a safety mechanism in situations where a local depolarization obstructs immediate excitation from the sarcolemma. Results obtained from this study also provide an explanation for the pattern of contractures observed in rippling muscle disease.

Investigation of a low cost method to quantify cosmetic defect.

For many patients, the motivation in seeking treatment is the improvement of their appearance rather than to correct an underlying skeletal deformity, so cosmetic concerns and the psychosocial impacts of adolescent idiopathic scoliosis are important factors in the clinical decision-making process. In the current environment of evidence based medicine there is a growing need to quantify back surface shape and general body asymmetry with the objective of producing an agreed scoring to be used in developing treatment plans and assessing outcomes but to date many clinics continue to rely on qualitative or expensive methods to describe cosmetic deformity. In November 2010, Microsoft® Corporation launched the low cost Kinect™ camera with 18 million units sold (as at January 2012) throughout the world. The device incorporates proprietary light coding technology that reconstructs the three dimensional location of an estimated 50,000 projected points illuminating objects within its field of view in approximately 1/30th of a second. The aim of the research was to investigate the capabilities of a low cost, reliable and inherently safe apparatus based on Kinect depth sensing and video technology to simultaneously acquire back surface shape and the locations of bony landmarks with the goal of providing data to describe cosmetic defect. Work has been completed using both the apparatus and a commercially available optical motion capture system (Vicon Motion Systems, Oxford, U.K.) to acquire data from a test object representing an unaffected human torso. Results were obtained to compare tri-dimensional bony landmark reconstruction accuracy and combined with analyses of point cloud data to describe back shape. Early indications are that the proposed apparatus has potential to be a clinically useful tool.

Augmented flap reconstruction of complex pressure ulcers using synthetic hybrid-scale fiber matrix.

INTRODUCTION: Flap reconstruction of pressure ulcers offers an important clinical means of decreasing morbidity in hospitalized patients. A new, novel method of managing pressure ulcer wounds uses a synthetic hybrid-scale fiber matrix prior to tissue flap reconstruction. This synthetic hybrid-scale fiber matrix is comprised of micron-scale and nanoscale fiber structure similar to that of human extracellular matrix and supports cell ingrowth, retention, and granulation tissue formation. OBJECTIVE: The primary objective of the present study was to examine use of the synthetic hybrid-scale fiber matrix as a means of encouraging granulation tissue within complex wounds to promote successful and lasting wound closure following flap reconstruction. MATERIALS AND METHODS: Patients included in this retrospective study had pressure ulcers that were not successfully managed with other wound therapies; in addition, these patients presented with various risk factors for postoperative complications. Before treatment, sharp debridement of the wound margins and wound bed was performed. Wounds were subsequently treated by applying synthetic hybrid-scale fiber matrix prior to flap reconstruction, based on physician assessment of wound status. The primary objective to include the synthetic hybrid-scale fiber matrix in the treatment approach of pressure ulcers in this case series was to ensure (1) integration to the wound bed prior to flap closure to encourage granulation tissue formation at a later time and (2) lasting successful wound closure following flap reconstruction. RESULTS: Overall, the patient outcomes indicated that the synthetic hybrid-scale fiber matrix was used to manage pressure ulcers successfully, with a wound closure rate of 90.9% (10 cases of complete wound closure and 1 case of 97.2% wound area reduction). Additionally, no complication related to the application of each synthetic hybrid-scale fiber matrix was reported. CONCLUSIONS: Application of synthetic hybrid-scale fiber matrix to the wound bed prior to flap closure promotes cellular ingrowth and granulation tissue formation, which promotes successful and lasting wound closure following flap reconstruction.

Validity of sagittal thoracolumbar curvature measurement using a non-radiographic surface topography method.

PURPOSE: To estimate the criterion validity of sagittal thoracolumbar spine measurement using a surface topography method in a clinical population against the gold standard and to estimate concurrent validity against two non-radiographic clinical tools. METHODS: In this cross-sectional validity study, thoracolumbar curvature was measured in adults with spinal conditions recruited from a specialist orthopaedic hospital. A surface topography method using a Kinect sensor was compared to three other measurement methods: spinal radiograph (gold standard), flexicurve and digital inclinometer. Correlation coefficients and agreement between the measurement tools were analysed. RESULTS: Twenty-nine participants (79% female) were included in criterion validity analyses and 38 (76% female) in concurrent validity analyses. The surface topography method was moderately correlated with the radiograph (r = .70, p < .001) in the thoracic spine, yet there was no significant correlation with the radiograph in the lumbar spine (r = .32, p = .89). The surface topography method was highly correlated with the flexicurve (rs = .91, p < .001) and digital inclinometer (r = .82, p < .001) in the thoracic spine, and highly correlated with the flexicurve (r = .74, p < .001) and digital inclinometer (r = .74, p < .001) in the lumbar spine. CONCLUSIONS: The surface topography method showed moderate correlation and agreement in thoracic spine with the radiograph (criterion validity) and high correlation with the flexicurve and digital inclinometer (concurrent validity). Compared with other non-radiographic tools, this surface topography method displayed similar criterion validity for kyphosis curvature measurement.

A longitudinal study of the arterio-venous fistula maturation of a single patient over 15 weeks.

Arterio-venous fistula creation is the preferred vascular access for haemodialysis, but has a large failure rate in the maturation period. Previous research, considering the remodelling mechanisms for failure-to-mature patients, has been limited by obtaining the patient-specific boundary conditions at only a few points in the patient history. Here, a non-invasive imaging system was used to reconstruct the three-dimensional vasculature, and computational fluid dynamics was used to analyse the haemodynamics for one patient over 15 weeks. The analysis suggested evidence of a control mechanism, which adjusts the lumen diameter to keep the wall shear stress near constant in the proximal regions of the vein and artery. Additionally, the vein and artery were shown to remodel at different growth rates, and the blood flow rate also saw the largest increase within the first week. Wall shear stress at time of creation may be a useful indicator for successful AVF maturation.

Subcellular Propagation of Cardiomyocyte ß-Adrenergic Activation of Calcium Uptake Involves Internal ß-Receptors and AKAP7.

ß-adrenergic receptor (ß-AR) signaling in cardiac myocytes is central to cardiac function, but spatiotemporal activation within myocytes is unresolved. In rabbit ventricular myocytes, ß-AR agonists or high extracellular [Ca] were applied locally at one end, to measure ß-AR signal propagation as Ca-transient (CaT) amplitude and sarcoplasmic reticulum (SR) Ca uptake. High local [Ca]o, increased CaT amplitude under the pipette faster than did ISO, but was also more spatially restricted. Local isoproterenol (ISO) or norepinephrine (NE) increased CaT amplitude and SR Ca uptake, that spread along the myocyte to the unexposed end. Thus, local [Ca]i decline kinetics reflect spatio-temporal progression of ß-AR end-effects in myocytes. To test whether intracellular ß-ARs contribute to this response, we used ß-AR-blockers that are membrane permeant (propranolol) or not (sotalol). Propranolol completely blocked NE-dependent CaT effects. However, blocking surface ß-ARs only (sotalol) suppressed only ∼50% of the NE-induced increase in CaT peak and rate of [Ca]i decline, but these changes spread more gradually than NE alone. We also tested whether A-kinase anchoring protein 7γ (AKAP7γ; that interacts with phospholamban) is mobile, such that it might contribute to intracellular spatial propagation of ß-AR signaling. We found AKAP7γ to be highly mobile using fluorescence recovery after photobleach of GFP tagged AKAP7γ, and that PKA activation accelerated AKAP7γ-GFP wash-out upon myocyte saponin-permeabilization, suggesting increased AKAP7γ mobility. We conclude that local ß-AR activation can activate SR Ca uptake at remote myocyte sites, and that intracellular ß-AR and AKAP7γ mobility may play a role in this spread of activation.

Effects of increased systolic Ca²âº and phospholamban phosphorylation during ß-adrenergic stimulation on Ca²âº transient kinetics in cardiac myocytes.

Previous studies demonstrated higher systolic intracellular Ca(2+) concentration ([Ca(2+)](i)) amplitudes result in faster [Ca(2+)](i) decline rates, as does ß-adrenergic (ß-AR) stimulation. The purpose of this study is to determine the major factor responsible for the faster [Ca(2+)](i) decline rate with ß-AR stimulation, the increased systolic Ca(2+) concentration levels, or phosphorylation of phospholamban. Mouse myocytes were perfused under basal conditions [1 mM extracellular Ca(2+) concentration ([Ca(2+)](o))], followed by high extracellular Ca(2+) (3 mM [Ca(2+)](o)), washout with 1 mM [Ca(2+)](o), followed by 1 µM isoproterenol (ISO) with 1 mM [Ca(2+)](o). ISO increased Ser(16) phosphorylation compared with 3 mM [Ca(2+)](o), whereas Thr(17) phosphorylation was similar. Ca(2+) transient (CaT) (fluo 4) data were obtained from matched CaT amplitudes with 3 mM [Ca(2+)](o) and ISO. [Ca(2+)](i) decline was significantly faster with ISO compared with 3 mM [Ca(2+)](o). Interestingly, the faster decline with ISO was only seen during the first 50% of the decline. CaT time to peak was significantly faster with ISO compared with 3 mM [Ca(2+)](o). A Ca(2+)/calmodulin-dependent protein kinase (CAMKII) inhibitor (KN-93) did not affect the CaT decline rates with 3 mM [Ca(2+)](o) or ISO but normalized ISO's time to peak with 3 mM [Ca(2+)](o). Thus, during ß-AR stimulation, the major factor for the faster CaT decline is due to Ser(16) phosphorylation, and faster time to peak is due to CAMKII activation.

Incidental finding of ileal gastrointestinal stromal tumour during prostate cancer staging with prostate-specific membrane antigen scan.

Prostate-specific membrane antigen (PSMA) positron emission tomography (PET)/computed tomography (CT) is used in managing and staging prostate cancer, but can identify other non-prostate pathology. We present the first reported case where small bowel gastrointestinal stromal tumour (GIST) has been incidentally identified on PSMA-PET scan and highlight the need for awareness of other pathology being identified on PSMA-PET/CT.

Ca sparks do not explain all ryanodine receptor-mediated SR Ca leak in mouse ventricular myocytes.

Diastolic Ca leak from the sarcoplasmic reticulum (SR) of ventricular myocytes reduces the SR Ca content, stabilizing the activity of the SR Ca release channel ryanodine receptor for the next beat. SR Ca leak has been visualized globally using whole-cell fluorescence, or locally using confocal microscopy, but never both ways. When using confocal microscopy, leak is imaged as "Ca sparks," which are fluorescent objects generated by the local reaction-diffusion of released Ca and cytosolic indicator. Here, we used confocal microscopy and simultaneously measured the global ryanodine-receptor-mediated leak rate (J(leak)) and Ca sparks in intact mouse ventricular myocytes. We found that spark frequency and J(leak) are correlated, as expected if both are manifestations of a common phenomenon. However, we also found that sparks explain approximately half of J(leak). Our strategy unmasks the presence of a subresolution (i.e., nonspark) release of potential physiological relevance.

Spontaneous Ca waves in ventricular myocytes from failing hearts depend on Ca(2+)-calmodulin-dependent protein kinase II.

Increased cardiac ryanodine receptor (RyR)-dependent diastolic SR Ca leak is present in heart failure and in conditions when adrenergic tone is high. Increasing Ca leak from the SR could result in spontaneous Ca wave (SCaW) formation. SCaWs activate the inward Na/Ca exchanger (NCX) current causing a delayed afterdepolarization (DAD), potentially leading to arrhythmia. Here we examine SCaWs in ventricular myocytes isolated from failing and healthy rabbit hearts. Myocytes from healthy hearts did not exhibit SCaWs under baseline conditions versus 43% of those exposed to isoproterenol (ISO). This ISO-induced increase in activity was reversed by inhibition of Ca-calmodulin-dependent protein kinase II (CaMKII) by KN93. Inhibition of cAMP-dependent protein kinase (PKA) by H89 had no observed effect. Of myocytes treated with forskolin 50% showed SCaW activity, attributable to a large increase in SR Ca load ([Ca](SRT)) versus control. At similar [Ca](SRT) (121muM) myocytes treated with ISO plus KN93 had significantly fewer SCaWs versus those treated with ISO or ISO plus H89 (0.2+/-0.28 vs. 1.1+/-0.28 and 1.29+/-0.39 SCaWs cell(-)(1), respectively). In myocytes isolated from failing hearts ISO induced an increase in the percentage of cells generating SCaWs vs. baseline (74% vs. 11%) with no increase in [Ca](SRT). Inhibiting CaMKII reversed this effect (14%). At similar [Ca](SRT) (71microM) myocytes treated with ISO or ISO plus H89 had significantly more SCaWs per cell vs. untreated (2.5+/-0.5; 1.6+/-0.7 vs. 0.36+/-0.3, respectively). Treatment with ISO plus KN93 completely abolished this effect. The evidence suggests the ISO-dependent increase in SCaW activity in both healthy and failing myocytes is CaMKII-dependent, implicating CaMKII in arrhythmogenesis.