Calcium movement in smooth muscle and evaluation of graded functional intercellular coupling.

Spontaneous activity of vascular smooth muscle is present in small arteries and some venous tissues like the hepatic portal vein. Whereas the ability to generate rhythmic membrane potential changes is expressed in a high number of primary oscillators, the generation of physiological tone and phasic activity requires synchronization of specialized pacemaker activity (Interstitial Cajal-like cells) by intercellular propagation and regeneration of excitation or a strong coupling mechanism of smooth muscle cells. The aim of this study was to deduce oscillator coupling by analyzing the spatiotemporal homogeneity of calcium oscillations within a native tissue preparation. Portal vein tissue was loaded with a calcium-sensitive dye (Fluo-3). By combining confocal microscopy and computation of spatial auto- and cross-correlation of the calcium signals, temporal and spatial coupling between cells was characterized. Spontaneous oscillations of calcium signals were measured at different predefined regions of interest. Cross-correlation analysis of these signals revealed that their damping was very similar in all directions of the investigated z-plane. In single experiments, improved cell-to-cell coupling was seen when noradrenaline (1-10 µM) was added to the bath-solution. With the chosen parameters of frame refresh, the velocity of signal propagation was faster than the maximum detectable velocity, but it could be estimated to exceed 0.1 mm/s. Correlative Network Analysis is a new and very useful tool to determine the functional coupling parameters of quasi-homogenous biological networks and their temporal changes. The action and significance of pharmacological modulators can be well studied on cellular and functional aspects with this newly introduced technique in biological sciences.

The sphingosine analog fingolimod (FTY720) enhances tone and contractility of rat gastric fundus smooth muscle.

BACKGROUND: Sphingosine and its metabolite sphingosine phosphate (S1P) regulate a multitude of biological functions, including the contractile state of smooth. Gastrointestinal side effects have been reported in patients treated with FTY720, a sphingosine analog that is approved for the treatment of multiple sclerosis. The aim of this study was to characterize the effects of FTY720 on rat gastric fundus smooth muscle under basal conditions and during activation induced by high-K+ solution. METHODS: Isometric contractions of isolated circular strips of gastric fundus smooth muscle were recorded using the organ bath method. The effects of FTY720 or vehicle were recorded under control conditions and in the presence of indomethacin, L-NAME, HA-1100, nifedipine, JTE-013, and suramin. Tone and contractions recorded in the presence of FTY720 or vehicle are reported as % of the amplitude of an initial high-K+ contraction obtained under control conditions. KEY RESULTS: From a concentration of 10 µmol L-1 onwards, FTY720 increased the tone, reaching 8.9% ± 7.5% at 100 µmol L-1 (P < .05). With indomethacin in the solution, the effects of FTY720 were enhanced (32.1% ± 7.7%; P < .001). The FTY720-induced increase in tone was abolished in the absence of extracellular Ca2+ and reduced by nifedipine, HA-1100, JTE-013, and suramin. Furthermore, FTY720 increased high-K+ contractions in the presence of indomethacin. CONCLUSIONS & INFERENCES: FTY720 increases tone and contractile responses to depolarization in gastric fundus smooth muscle by triggering calcium entry and calcium sensitization in a S1P receptor-dependent manner. Taken together, the experimental results presented in this work suggest that FTY720 may increase gastric tone and contractility in patients.

[Surgical techniques in mitral valve diseases. Reconstruction and/or replacement]. / Operative Techniken bei Mitralklappenerkrankungen. Rekonstruktion und/oder Ersatz.

Mitral valve (MV) disease is one of the most common heart valve diseases. The surgical and interventional treatment for MV disease requires a multidisciplinary approach. For primary mitral valve regurgitation (MVR) surgical MV repair is the treatment of choice, which can be performed with an excellent outcome and long-term survival in reference centers. The surgical technique used for MV repair depends on the pathological mechanism, the morphological dimensions of the MV, the operative risk and the expertise of the cardiac surgeon. The surgical and interventional treatment of secondary MVVR is the subject of on-going discussions. In patients with moderate secondary MVR undergoing coronary artery bypass grafting, concomitant MV repair should be performed. In the presence of severe secondary MR with risk factors for failure of MV repair, patients should consider having MV replacement. In the rare cases of patients presenting with mitral valve stenosis (MVS) MV repair can be considered in young patients and who are most often treated with MV replacement. The choice between biological or mechanical MV replacement depends on the pathophysiology, the comorbidities, the amount of anticoagulation necessary and the age of the patient. New percutaneous techniques for MV replacement offer new treatment options for reoperation in high-risk patients.

Phenytoin inhibits contractions of rat gastrointestinal and portal vein smooth muscle by inhibiting calcium entry.

BACKGROUND: Phenytoin is widely used as a second-line treatment for status epilepticus. Besides its well-known cardiac pro-arrhythmogenicity, side effects on other organ systems have received less attention. METHODS: This study investigates the effects of phenytoin on gastrointestinal tissue function using an in vitro model of smooth muscle preparations from rats by combining registrations of pharmacological effects on mechanical contractions, electric field potentials, and dynamic intravital fluorescence microscopy. KEY RESULTS: When added to the bathing solution at a concentration of 30 µM, phenytoin reduced the frequency of spontaneous activity significantly in antrum and portal vein preparations to 72.2 ± 36.5% (p = 0.022) and 80.7 ± 24.4% (p = 0.037) of control values, respectively. At a concentration of 100 µM, the height of spontaneous contractions declined to 9.8 ± 19.6% (p = 0.005) (antrum), 15.7 ± 28.2% (p = 0.004) (portal vein), and 31.8 ± 31.3% (p = 0.005) (colon) in comparison to the control conditions before the application of phenytoin. Depolarization triggered increases in calcium dependent fluorescence signals were reduced by 52.8 ± 39.1% (p = 0.012) The inhibition of spontaneous activity caused by phenytoin was reduced in the presence of the L-type calcium channel agonist BAY K8644(-). CONCLUSIONS & INFERENCES: Phenytoin exerts strong inhibitory effects on the spontaneous and stimulated contractile activity of smooth muscles from both the upper and lower gastrointestinal tract. The mechanism underlying this effect is not related to the sodium channel blocking activity of phenytoin, but is rather caused by an inhibition of calcium entry through voltage dependent L-type calcium channels. The results of this study should raise vigilance to gastrointestinal complications in patients treated with phenytoin.

[Fatigue in patients with multiple sclerosis--pathogenesis, clinical picture, diagnosis and treatment]. / Fatigue bei Patienten mit Multipler Sklerose--Pathogenese, Klinik, Diagnostik und Therapie.

Fatigue is a frequent and restricting symptom of multiple sclerosis (MS). Starting from its pathogenetic mechanisms, the article develops an approach to the differential diagnosis of fatigue in MS patients. Over the past years, the use of functional imaging techniques has given important information on the mechanisms of this highly variable clinical picture. Considering our improved understanding of the interdependency of immune pathology and the clinical presentation of neuropsychological disorders, the relationship between immunomodulatory treatments and fatigue is receiving increased attention. Therefore, this article not only reports on the most recent data on pharmacological, physical and psychological interventions in the symptomatic treatment of fatigue, but also puts a special accent on data concerning the interactions between the rapidly growing number of immunomodulatory treatments in MS.

Characterization of ion currents of murine CD117(pos) stem cells in vitro and their modulation under AT2 R stimulation.

AIM: Hematopoietic stem cells, especially CD117(pos) cells, have been found to possess a regenerative potential in various tissues, in particular cardiac muscle. However, the characterization of the relevant ion currents of stem cells prior to implantation lacks documentation. Activation of angiotensin II type 2 receptor (AT2 R) can lead to further cell differentiation and receptor auto-expression and might thus influence electrophysiological properties of CD117(pos) stem cells. This study was designed to functionally characterize membrane currents of CD117(pos) cells under normal and AT2 R-stimulated conditions. METHODS: CD117(pos) murine bone marrow stem cells were isolated with MACS technique and stimulated for the AT2 R with angiotensin II and losartan for 3-5 days prior to patch-clamp measurements. RT-PCR was used to determine channel expression. Endothelial properties were analysed with immunocytochemistry and acLDL uptake assay. RESULTS: A well-expressed inward rectifying current (IKir ) was identified in cultured CD117(pos) cells. Furthermore, a ZD 7288 (HCN channel blocker)-sensitive current component was isolated. Voltage-dependent potassium currents and chloride currents were less expressed. A small fraction of cells demonstrated voltage- and time-dependent inward currents. In AT2 R-stimulated cells inward rectifying the hyperpolarization-induced inward currents were slightly attenuated on the translational level but showed increased mRNA expression. Cultured CD117(pos) cells express CD31 and VEGFR-2 and significantly increased the uptake of acLDL. CONCLUSIONS: CD117(pos) cells do not have properties of action potential-generating cells and moderately change their excitability during AT2 R stimulation. Electrophysiological and molecular properties of control and AT2 R-stimulated cells point to a differentiation to vascular endothelial cells. This could increase beneficial vascularization in injured tissues.

Towards patient-specific finite-element simulation of MitralClip procedure.

MitralClip is a novel minimally invasive procedure to treat mitral valve (MV) regurgitation. It consists in clipping the mitral leaflets together to close the regurgitant hole. A careful preoperative planning is necessary to select respondent patients and to determine the clipping sites. Although preliminary indications criteria are established, they lack prediction power with respect to complications and effectiveness of the therapy in specific patients. We propose an integrated framework for personalized simulation of MV function and apply it to simulate MitralClip procedure. A patient-specific dynamic model of the MV apparatus is computed automatically from 4D TEE images. A biomechanical model of the MV, constrained by the observed motion of the mitral annulus and papillary muscles, is employed to simulate valve closure and MitralClip intervention. The proposed integrated framework enables, for the first time, to quantitatively evaluate an MV finite-element model in-vivo, on eleven patients, and to predict the outcome of MitralClip intervention in one of these patients. The simulations are compared to ground truth and to postoperative images, resulting in promising accuracy (average point-to-mesh distance: 1.47 +/- 0.24 mm). Our framework may constitute a tool for MV therapy planning and patient management.

The Clara cell: a "Third Reich eponym"?

German anatomist Max Clara (1899-1966) described the "Clara cell" of the bronchiolar epithelium in 1937. The present article investigates Clara's relationship with National Socialism, as well as his use of tissue from executed prisoners for research purposes, details about both of which are largely unknown to date. Our methodology for the present study focussed on analysis of material from historical archives and the publications of Clara and his co-workers. Clara was appointed as Chair of Anatomy at Leipzig University (Leipzig, Germany) in 1935. He owed his career, at least in part, to Nazi support. He was an active member of the Nazi party (Nationalsozialistische Deutsche Arbeiterpartei (NSDAP)) and engaged in university politics; this included making anti-Semitic statements about other academics in appointment procedures. Nevertheless, he also supported prosecuted colleagues. Much of Clara's histological research in Leipzig, including his original description of the bronchial epithelium, was based on tissue taken from prisoners executed in nearby Dresden (Germany). Max Clara was an active and outspoken Nazi and his histological research exploited the rising number of executions during the Nazi period. Clara's discovery is thus linked to the Nazi system. The facts given in the present paper invite discussion about the eponym's neglected history and its continued and problematic use in medical terminology.

Electrodynamic smooth muscle sphincter: development and biomechanical evaluation of a novel porcine artificial smooth muscle sphincter in a new in vitro stoma simulator.

AIM: Many authors have suggested that the activity of the enteric inhibitory nerves is important in regulating normal gastrointestinal motility and inducing smooth muscle relaxation. Hitherto, no experimental or clinical models exist that transfer these physiological aspects to creating an autologous artificial sphincter for the treatment of major incontinence. Therefore, this study was performed to determine the contractile and relaxant capacity of gastrointestinal muscle types and to investigate the efficiency of a novel smooth muscle sphincter, based on the non-adrenergic, non-cholinergic (NANC) receptive relaxation under electrical field stimulation (EFS). METHODS: For the first step, the isometric tension from isolated circular porcine fundus and colon muscle strips was recorded during pharmacological stimulation (TTX, L-NNA and atropine) and EFS. As a result, a continent electrodynamic smooth muscle sphincter (ESMS) was created by wrapping a fundus muscle flap around an isolated segment of porcine distal colon. The EFS of the free nerve fibers of the flap was realized using a circular platinum wire electrode. Parameters such as threshold of continence, intra/preluminal pressure and fluid passage were analyzed in a newly designed in vitro stoma simulator. RESULTS: Electrical field stimulation produced a maximal and voltage-dependent fundus relaxation to --12.4 mN/mm(2) (frequency of 40 Hz, pulse duration, train duration and voltage of 5 ms, 1 s and 60 mA respectively), which were abolished by N-nitro-L -arginine (L-NNA; 10(-4) M) in a dose-dependent manner, confirming that relaxant responses were mediated by NANC nerves. The results of eight ESMS showed that circular electrical stimulation of the muscle flap caused muscle relaxation with a concomitant and effective reduction in the occlusion pressure. CONCLUSION: The NANC-induced relaxation mechanism of porcine fundus preparations could be transferred to an efficient smooth muscle sphincter with a high threshold of continence and electrically controlled defecation.

4-aminopyridine affects rat arterial smooth muscle BK(Ca) currents by changing intracellular pH.

The hypothesis whether or not 4-AP can affect vascular smooth muscle BK(Ca) currents was tested using the patch-clamp technique, pH- and calcium-fluorimetry, and freshly isolated rat arterial smooth muscle cells. Application of 4-AP reversibly inhibited BK(Ca) currents at an intracellular calcium ([Ca](i)) of 250 nM with a half-block of 2. 5 mM at +50 mV. The presence of 2 microM thapsigargin, 10 microM heparin, and 10 microM ryanodine did not alter the effect of 4-AP on BK(Ca) currents at [Ca](i) 250 nM. At [Ca](i)<100 nM 4-AP did not inhibit BK(Ca) currents. Application of 4-AP to the intracellular or extracellular side of excised BK(Ca) channels did not alter channel activity or channel amplitude. Replacement of the pH-sensitive calcium buffer EGTA by the pH-insensitive calcium buffer BAPTA in the intracellular solution turned the 4-AP-induced inhibition of BK(Ca) currents into a stimulation at [Ca](i) 250 nM. Application of 4-AP to single cells increased intracellular pH, which was accompanied by a reduction of [Ca](i) in EGTA-loaded cells and a stable [Ca](i) in BAPTA-loaded cells. Thus, these results suggest that in isolated vascular smooth muscle cells at [Ca](i)>100 nM 4-AP affects BK(Ca) currents via an alteration of intracellular pH.

Protein kinase C reduces the KCa current of rat tail artery smooth muscle cells.

The hypothesis that protein kinase C (PKC) is able to regulate the whole cell Ca-activated K (KCa) current independently of PKC effects on local Ca release events was tested using the patch-clamp technique and freshly isolated rat tail artery smooth muscle cells dialyzed with a strongly buffered low-Ca solution. The active diacylglycerol analog 1,2-dioctanoyl-sn-glycerol (DOG) at 10 microM attenuated the current-voltage (I-V) relationship of the KCa current significantly and reduced the KCa current at +70 mV by 70 +/- 4% (n = 14). In contrast, 10 microM DOG after pretreatment of the cells with 1 microM calphostin C or 1 microM PKC inhibitor peptide, selective PKC inhibitors, and 10 microM 1,3-dioctanoyl-sn-glycerol, an inactive diacylglycerol analog, did not significantly alter the KCa current. Furthermore, the catalytic subunit of PKC (PKCC) at 0.1 U/ml attenuated the I-V relationship of the KCa current significantly, reduced the KCa current at +70 mV by 44 +/- 3% (n = 17), and inhibited the activity of single KCa channels at 0 mV by 79 +/- 9% (n = 6). In contrast, 0.1 U/ml heat-inactivated PKCC did not significantly alter the KCa current or the activity of single KCa channels. Thus these results suggest that PKC is able to considerably attenuate the KCa current of freshly isolated rat tail artery smooth muscle cells independently of effects of PKC on local Ca release events, most likely by a direct effect on the KCa channel.

Signal transduction in cavernous smooth muscle.

Knowledge of intracellular signal propagation in smooth-muscle tone regulation is of major importance to the understanding of both the physiology of erection and the pathophysiology of erectile dysfunction and the development of new and selective pharmacological agents in the treatment of erectile dysfunction. Cavernous smooth-muscle tone depends heavily on the amount of intracellular free Ca2+. In the resting state the sarcoplasmic free Ca2+ amounts to about 120-270 nM, whereas in the extracellular fluid the Ca2+ level is in the range of 1.5-2 mM. Electromechanical and pharmacomechanical coupling induces an increase in the levels of free sarcoplasmic Ca2+ by a factor of 2-3 to 550-700 nM that triggers myosin phosphorylation and subsequent smooth muscle contraction. In this case, modulation of membrane-bound ion channels and regulation of the intracellular second-messenger system are attractive and feasible targets for pharmacological intervention. Besides the amount of free sarcoplasmic Ca2+, smooth-muscle tone is also modulated by the regulation of Ca2+ sensitivity ("Ca-sensitization") and Ca(2+)-independent contraction processes.

Multiple types of ion channels in cavernous smooth muscle.

The excitation process of the smooth muscle of corpus cavernosum is important to the erectile process. single-cell electrophysiology performed during the last decade has given deep insights into the different current components participating in that process. However, the existence of a tremendous amount of literature might be confusing for the nonspecialist in the field of smooth-muscle excitation and, especially, in the excitation of corpus cavernosum. In a compact form, this paper gives an overview on significant ionic currents as well as their ability to change the membrane potential and to enhance or inhibit calcium influx for the modulation of smooth-muscle tone.

Electrical and chemical control of smooth muscle activity of rabbit corpus cavernosum in vitro.

OBJECTIVES: This study sought to further elucidate the regulation of cavernous smooth muscle tone and to characterize mechanisms of cavernous activation and relaxation. METHODS: In isolated strips of rabbit corpus cavernosum, extracellular electrical and mechanical activity were recorded simultaneously before and after pharmacologic stimulation. RESULTS: Spontaneous mechanical activity was characterized by fast phasic contractions (frequency 6 to 30 min-1) associated with fluctuations of the extracellular electrical signals. Phasic activity was increased by blockade of potassium channels or by moderate activation of L-type calcium channels. Faster spikelike fluctuations occurred in the electrical activity, indicating the existence of spike discharges. All mechanical and electrical fluctuations were completely abolished by blockade of L-type calcium channels with nifedipine. CONCLUSIONS: Our results indicate that cavernous smooth muscle tone is regulated by both phasic and tonic activation mechanisms caused by the opening of L-type calcium channels and calcium influx through chemically controlled calcium influx/release.

[Functional electromyostimulation of the penile corpus cavernosum (FEMCC)]. Initial results of a new therapeutic option of erectile dysfunction]. / Funktionelle Elektromyostimulation des Corpus cavernosum penis (FEMCC). Erste Ergebnisse einer neuen therapeutischen Option bei erektiler Dysfunktion.

Transcutaneous application of low-frequency electric current in the treatment of partially or temporarily denervated striated muscles is widely used to prevent or treat muscular atrophy. Due to the high regenerative capacity of smooth muscle cells, this approach should be beneficial in the treatment of diseases with smooth muscle degeneration due to partial denervation. Our study was done to evaluate the possible beneficial effect of transcutaneous application of low-frequency electric current to the corpus cavernosum penis in the treatment of erectile dysfunction. After a comprehensive work-up, 22 patients with chronic erectile dysfunction (21/22 vasoactive nonresponders) received daily (3-5 x 20 min) transcutaneous functional electromyostimulation of the corpus cavernosum smooth muscles (FEMCC; zero line symmetric impulses of trapezoid shape, two-channel device with alternating stimulations, f = 10-20 Hz for channel I and 20-35 Hz for channel II; t(i) = 100-2000 microseconds, approx. 12 mA, rise time 0.5 s, stimulation time 5 s per channel, interval between stimulations 0.5 s). Five of 22 patients (23%) regained full spontaneous erections and another three (14%) responded to vasoactive drugs after FEMCC. Fourteen were FEMCC failures, including two who subjectively 'improved'. In a similar group of patients evaluated during the same period but receiving no therapy, no spontaneous improvement of the erectile function was observed. Our preliminary results suggest that FEMCC is feasible and results in an improvement of the erectile capacity in a significant proportion (37%) of patients. Further studies will be carried out to corroborate our results, to improve stimulation parameters and to evaluate selection criteria for FEMCC.

Effects of BRL55834 in rat portal vein and bovine trachea: evidence for the induction of a glibenclamide-resistant, ATP-sensitive potassium current.

1. The effects of the benzopyran K-channel opener, BRL55834, on mechanical activity in bovine trachealis and rat portal vein were studied together with membrane currents in freshly-isolated single cells derived from these tissues. 2. BRL55834 (3 nM-1 microM) produced a concentration-dependent relaxation of bovine trachealis precontracted with 100 microM histamine and reduced the spontaneous mechanical activity of rat portal veins, effects which were antagonized by glibenclamide (1-10 microM) but were not reversible on washing. In contrast, charybdotoxin (250 nM) did not modify the spasmolytic effect of BRL55834 in bovine trachealis. 3. BRL55834 (10 nM-10 microM) did not relax segments of bovine trachealis precontracted with 80 mM KCl. 4. In some freshly-isolated single cells from bovine trachealis held at -10 mV, BRL55834 (3 microM) induced a time-independent outward K-current which was partially resistant to inhibition by glibenclamide (10 microM). In other cells, a very noisy, outwardly-rectifying and charybdotoxin-sensitive current developed in the presence of BRL55834 (3 microM) and in time-matched control cells. 5. In freshly-isolated single cells from rat portal vein held at -10 mV, BRL55834 (3 microM) induced a time- and calcium-independent outward K-current which was partially resistant (approximately 25% inhibition at +40 mV) to subsequent inhibition by glibenclamide (10 microM). In contrast, levcromakalim induced a time-independent outward K-current which was completely inhibited by glibenclamide 10 microM. 6. With the non-hydrolysable ATP analogue, AMP-PCP (5 mM), in the pipette, the ability of BRL55834 to induce a time-independent K-current in portal vein cells was markedly reduced (approximately 80% inhibition at +40 mV) whereas the effects of 10 microM levcromakalim were totally inhibited. 7. The glibenclamide-resistant current component induced by BRL55834 was totally inhibited by phentolamine (100 microM), a concentration that had no effect on the peak current (IBK(Ca)) induced by NS1619 (33 microM). 8. Stationary fluctuation analysis of the noise associated with the glibenclamide-insensitive K-current induced by BRL55834 in rat portal vein cells indicated that the unitary current flowing through the underlying channels was 0.26 pA at -10 mV, a value inconsistent with the involvement of BKCa. 9. It is concluded that the relaxations of both bovine trachea and rat portal vein produced by BRL55834 are associated with the opening of K-channels. These are probably identical to the ATP-sensitive K-channel opened by levcromakalim, although the involvement of an additional K-channel cannot be excluded. The reduced sensitivity of the BRL55834-induced changes to glibenclamide and toAMP-PCP may result from avid binding of BRL55834 to its site of action.

Functional electromyostimulation of the corpus cavernosum penis--preliminary results of a novel therapeutic option for erectile dysfunction.

Transcutaneous application of low-frequency electric current in the treatment of partially or temporarily denervated striated muscles is widely used to prevent or treat muscular atrophy. Due to the high regenerative capacity of smooth-muscle cells, this approach should be beneficial in the treatment of diseases with smooth-muscle degeneration due to partial denervation. Our study was done to evaluate the possible beneficial effect of transcutaneously applied low-frequency electric current on the corpus cavernosum penis in the treatment of erectile dysfunction. After a comprehensive workup, 21 patients with chronic erectile dysfunction (20/21 vasoactive nonresponders) received daily (3-5 x 20 min) transcutaneous functional electromyostimulation of the corpus cavernosum smooth muscles [FEMCC; zero-line symmetric impulses of trapezoid shape, 2-channel device with alternating stimulations; frequency (f), 10-20 Hz for channel I and 20-35 Hz for channel II; impulse duration (ti), 100-150 microseconds; approx. 12 mA; rise time, 0.5 s; stimulation time, 5 s/channel; pause between stimulations, 0.5 s. In all, 4/21 patients (19%) regained full spontaneous erections and another 3/21 (14%) responded to vasoactive drugs after FEMCC. Overall, 14/21 were FEMCC failures, including 2 who subjectively "improved." In a similar group of patients who were evaluated during the same period but received no therapy, no spontaneous improvement in erectile function was observed.(ABSTRACT TRUNCATED AT 250 WORDS)

Ion channel modulation by NS 1619, the putative BKCa channel opener, in vascular smooth muscle.

1. The effects of NS 1619, the putative BKCa channel opener, were investigated on rat intact portal veins and on single smooth muscle cells enzymatically separated from the same tissue. 2. Under whole-cell patch clamp conditions with K-rich pipettes, exposure of single cells held at -10 mV to NS 1619 (10-33 microM) induced a noisy, outward current which reached a maximum (33 microM NS 1619; mean 35.8 +/- 17 pA, n = 8) within about 6 min. 3. On stepping to test potentials (range -50 to +50 mV) from a holding potential of -10 mV, the NS 1619-induced noisy current exhibited time-dependent activation and marked outward rectification. 4. The stimulation of outward currents by NS 1619 at -10 mV was independent of the presence of Ca2+ in the bath or pipette solutions but was antagonized by either charybdotoxin (250 nM) or penitrem A (100 nM) in the bath solution. 5. Stationary fluctuation analysis of the noisy current induced by NS 1619 at -10 mV yielded a value of 70 +/- 8 pS (n = 4) (under the quasi-physiological conditions of the experiment) for the unitary conductance of the channel involved. 6. At -10 mV, NS 1619 (10-33 microM) rapidly inhibited spontaneous transient outward currents. 7. With a holding potential of -90 mV, NS 1619 (10-33 microM) produced a reduction of outward currents evoked by depolarizing steps to +50 mV, an effect associated with marked inhibition of the delayed rectifier current, IK(V). 8. NS 1619 (3-100 microM) produced a concentration-dependent inhibition of spontaneous activity in rat portal vein characterized by a reduction in the amplitude and duration of the tension waves. This inhibition was slightly potentiated in the presence of either charybdotoxin (250 nM) or penitrem A (1 microM). NS 1619 also totally inhibited contractions of rat aorta induced by KCl (both 20 mM and 80 mM). 9. Under whole-cell recording conditions and using Cs-rich pipettes, Ca-currents evoked in portal vein cells by stepping from a holding potential of - 90 mV to test potentials in the range - 30 to + 50 mV were totally inhibited in the presence of 33 JAM NS 1619.10. NS 1619 (33 JAM) inhibited the induction of IK(ATP) by levcromakalim (10 JAM).11. It is concluded that NS 1619 activates the large conductance, Ca2+-sensitive channel, BKca and over the same concentration range it inhibits both KV and L-type Ca-channels. The observed NS 1619-induced mechanical inhibition in rat portal vein and aorta seems most likely to be due to the observed inhibition of Ca-currents.

KATP channels and basal coronary vascular tone.

After reviewing recent experimental work from various laboratories we have come to the following conclusions. (1) An increase in transmural pressure causes depolarisation of coronary arterioles, which increases smooth muscle tone. Under these conditions the opening of KATP channels can induce a much larger change in membrane potential than in relaxed arteries. Furthermore, the rate of ATP hydrolysis by contractile proteins, and thus the submembrane nucleotide concentrations, might also be changed in the presence of myogenic tone. Therefore care should be taken when extrapolating patch clamp results from isolated coronary smooth muscle cells to the function of KATP channels in vivo. (2) The opening of KATP channels is increased in situations related to energy imbalance, such as hypoxia, adenosine release, intracellular acidification, and lactate accumulation. However, there is increasing evidence that KATP channels also contribute to the setting of the membrane potentials of coronary smooth muscle cells under normoxic conditions. Thus the modulation of KATP channels by intracellular metabolites and by vasoactive autacoids may play an important role in the regulation of coronary blood flow even in the presence of normal intracellular ATP concentrations. (3) The smooth muscle cells of coronary terminal arterioles form an electrical syncytium. The opening of a new KATP channels in smooth muscle cells of a terminal arterioles might induce a spatially homogeneous hyperpolarisation of the entire arteriole. The resulting homogeneous decrease in the tone of the coronary smooth muscle cells of the arteriole may induce a considerable change in vascular resistance.(ABSTRACT TRUNCATED AT 250 WORDS)