Relationships among norepinephrine levels, exercise capacity, and chronotropic responses in heart failure patients.

In heart failure (HF) patients, the pathophysiological mechanisms of severe exercise intolerance and impaired exercise capacity are related to both central and peripheral abnormalities. The central abnormalities in HF patients include impaired cardiac function and chronotropic incompetence (CI). Indeed, CI, the inability to adequately increase heart rate (HR) from rest to exercise often exhibited by HF patients, is related to activation of the sympathetic nervous system (SNS) yielding a rise in circulating norepinephrine (NE). CI may result from downregulation of ß-adrenergic receptors, ß-blocker usage, high baseline HR, or due to a combination of factors. This paper discusses the role of elevated NE in altering chronotropic responses in HF patients and consequently resulting in impaired exercise capacity. We suggest that future research should focus on the potential treatment of CI with rate-adaptive pacing, using a sensor to measure physical activity, without inducing deleterious hormonal activation of the sympathetic system.

Acute aerobic activity enhances response inhibition for less than 30min.

Acute exercise appears to facilitate certain aspects of cognitive processing. The possibility that exercise may lead to more efficient inhibitory processes is of particular interest, owing to the wide range of cognitive and motor functions that inhibition may underlie. The purpose of the present study was to examine the immediate and the delayed effect of acute aerobic exercise on response inhibition, motor planning, and eye-hand coordination in healthy active adults. Forty healthy and active participants (10 females) with a mean age of 51.88±8.46years performed the Go-NoGo test (response inhibition) and the Catch Game (motor planning and eye-hand coordination) before, immediately after, and following a 30-min recovery period in two conditions: a moderate-intensity aerobic session and a control session. In 2-way repeated measures ANOVAs (2 treatments×3 times) followed by contrast comparisons for post hoc analyses, significant pre-post interactions - indicating improvements immediately following exercise but not following the control condition - were observed in the Go-NoGo measures: Accuracy, Reaction Time, and Performance Index, but not in the Catch Game. In the post-follow-up interaction a deterioration was observed in Performance Index, and a trend of deterioration in Accuracy and Reaction Time. The conclusion was that a single session of moderate-intensity aerobic exercise facilitates response inhibition, but not motor planning or eye-hand coordination, in middle-aged healthy active adults. On the other hand, the improvement does not last 30min following a recovery period. Further studies are needed to examine the duration of the inhibitory control benefits and the accumulative effect of a series of acute exercise bouts, as well as to determine the brain networks and/or neurotransmitter systems most affected by the intervention.

Remote Pilates Training Is Effective in Improving Physical Fitness in Healthy Women: A Randomized Controlled Study.

Despite its positive impact on physical and mental well-being, adults may refrain from performing regular physical activity, due to inadequate time, accessibility, or funds. Yet remote platforms could overcome such obstacles and increase participation. This study evaluated the effectiveness of remote-synchronous group-Pilates classes compared to in-studio classes in healthy sedentary women. In a randomized controlled design, 40 women, aged 20-45, were assigned to a Zoom or studio group-Pilates training. The intervention included twice-weekly 45 min sessions over an eight-week period. Attendance (adherence) was recorded, and the participants completed physical motor tests (plank, curl-up, stork, push-up, and V-sit and reach), Profile of Mood State Surveys, and Nordic Musculoskeletal Pain Questionnaires. Evaluations were performed at baseline, mid-intervention (4 weeks), and post intervention (8 weeks). Adherence to training was high in the Zoom and studio groups (80% and 74%, respectively). Improvements in physical motor tests were seen in both groups following the Pilates interventions, thereby indicating the effectiveness of group-Pilates Zoom training. In conclusion, remote online physical activity such as Pilates offers a good alternative to in-studio trainings, as a means for improving physical fitness and promoting a healthy lifestyle in adults, by offering a more accessible and less timely alternative to in-studio physical activity programs.

Rearrangements in the relative orientation of cytoplasmic domains induced by a membrane-anchored protein mediate modulations in Kv channel gating.

Interdomain interactions between intracellular N and C termini have been described for various K(+) channels, including the voltage-gated Kv2.1, and suggested to affect channel gating. However, no channel regulatory protein directly affecting N/C interactions has been demonstrated. Most Kv2.1 channel interactions with regulatory factors occur at its C terminus. The vesicular SNARE that is also present at a high concentration in the neuronal plasma membrane, VAMP2, is the only protein documented to affect Kv2.1 gating by binding to its N terminus. As its binding target has been mapped near a site implicated in Kv2.1 N/C interactions, we hypothesized that VAMP2 binding to the N terminus requires concomitant conformational changes in the C terminus, which wraps around the N terminus from the outside, to give VAMP2 access. Here, we first determined that the Kv2.1 N terminus, although crucial, is not sufficient to convey functional interaction with VAMP2, and that, concomitant to its binding to the "docking loop" at the Kv2.1 N terminus, VAMP2 binds to the proximal part of the Kv2.1 C terminus, C1a. Next, using computational biology approaches (ab initio modeling, docking, and molecular dynamics simulations) supported by molecular biology, biochemical, electrophysiological, and fluorescence resonance energy transfer analyses, we mapped the interaction sites on both VAMP2 and Kv2.1 and found that this interaction is accompanied by rearrangements in the relative orientation of Kv2.1 cytoplasmic domains. We propose that VAMP2 modulates Kv2.1 inactivation by interfering with the interaction between the docking loop and C1a, a mechanism for gating regulation that may pertain also to other Kv channels.

Does Photobiomodulation Therapy Enhance Maximal Muscle Strength and Muscle Recovery?

Photobiomodulation has been shown to improve tissue and cell functions. We evaluated the influence of photobiomodulation, using a B-Cure laser, on: 1) maximal performance, and 2) muscle recovery after resistance exercise. Two separate crossover randomized double-blinded placebo-controlled trials were conducted. Sixty healthy physical education students (28 men, 32 women), aged 20-35, were recruited (30 participants for each trial). Participants performed two interventions for each experiment, with real lasers (GaAlAs, 808 nm) on three quadricep locations in parallel (overall treatment energy of ~150J) or sham (placebo) treatment. In the first experiment muscle total work (TW) and peak torque (PT) were measured by an isokinetic dynamometer in five repetitions of knee extension, and in the second experiment muscle recovery was measured after the induction of muscle fatigue by evaluating TW and PT in five repetitions of knee extension. There were no differences between treatments (real or sham) regarding the TW (F(1,28) = 1.09, p = .31), or PT (F(1,29) = .056, p = .814). In addition, there was no effect of photobiomodulation on muscle recovery as measured by the TW (F(1,27) = .16, p = .69) or PT (F(1,29) = .056, p = .814). Applying photobiomodulation for 10 min immediately before exercise did not improve muscle function or muscle recovery after fatigue.

Prediction of the Wingate anaerobic mechanical power outputs from a maximal incremental cardiopulmonary exercise stress test using machine-learning approach.

The Wingate Anaerobic Test (WAnT) is a short-term maximal intensity cycle ergometer test, which provides anaerobic mechanical power output variables. Despite the physiological significance of the variables extracted from the WAnT, the test is very intense, and generally applies for athletes. Our goal, in this paper, was to develop a new approach to predict the anaerobic mechanical power outputs using maximal incremental cardiopulmonary exercise stress test (CPET). We hypothesized that maximal incremental exercise stress test hold hidden information about the anaerobic components, which can be directly translated into mechanical power outputs. We therefore designed a computational model that included aerobic variables (features), and used a new computational \ predictive algorithm, which enabled the prediction of the anaerobic mechanical power outputs. We analyzed the chosen predicted features using clustering on a network. For peak power (PP) and mean power (MP) outputs, the equations included six features and four features, respectively. The combination of these features produced a prediction model of r = 0.94 and r = 0.9, respectively, on the validation set between the real and predicted PP/MP values (P< 0.001). The newly predictive model allows the accurate prediction of the anaerobic mechanical power outputs at high accuracy. The assessment of additional tests is desired for the development of a robust application for athletes, older individuals, and/or non-healthy populations.

The Acute Effect of Exercise on Executive Function and Attention: Resistance Versus Aerobic Exercise.

Acute aerobic exercise was shown to enhance such cognitive functions as executive function (EF) and attention. Acute resistance exercise was also shown to enhance cognitive functions, however, only few studies directly compared these two exercise modalities. The aim of this study was to evaluate the acute effect of a typical moderate intensity resistance exercise session as compared to a typical moderate intensity aerobic session, on executive function and attention. A counterbalanced repeated measures experimental design was applied. Forty physical education students (21 women; 19 men, age = 25.7±2.84 years) were tested before and after three sessions: aerobic, resistance, and control. Each session consisted of 30 minutes of exercise or a rest. Executive function and attention were assessed by components of the computerized Stroop Catch game and Go-NoGo cognitive tests. A two-way ANOVA showed a greater increase in attention scores after the resistance sessions (p < .05) compared to the control condition. Attention scores in the aerobic sessions showed a trend toward improvement but did not reach statistical significance. Scores of EF significantly increased, both after the resistance session and the aerobic session (p < .05), but not after rest in the control condition. Our findings show that an acute session of resistance exercise increased both Attention and EF test scores, while an aerobic exercise session improved only the EF scores.

K+ channel facilitation of exocytosis by dynamic interaction with syntaxin.

Kv channels inhibit release indirectly by hyperpolarizing membrane potential, but the significance of Kv channel interaction with the secretory apparatus is not known. The Kv2.1 channel is commonly expressed in the soma and dendrites of neurons, where it could influence the release of neuropeptides and neurotrophins, and in neuroendocrine cells, where it could influence hormone release. Here we show that Kv2.1 channels increase dense-core vesicle (DCV)-mediated release after elevation of cytoplasmic Ca2+. This facilitation occurs even after disruption of pore function and cannot be explained by changes in membrane potential and cytoplasmic Ca2+. However, triggering release increases channel binding to syntaxin, a secretory apparatus protein. Disrupting this interaction with competing peptides or by deleting the syntaxin association domain of the channel at the C terminus blocks facilitation of release. Thus, direct association of Kv2.1 with syntaxin promotes exocytosis. The dual functioning of the Kv channel to influence release, through its pore to hyperpolarize the membrane potential and through its C-terminal association with syntaxin to directly facilitate release, reinforces the requirements for repetitive firing for exocytosis of DCVs in neuroendocrine cells and in dendrites.

Formation of the full SNARE complex eliminates interactions of its individual protein components with the Kv2.1 channel.

Previously, we have demonstrated physical and functional interactions of the voltage-gated potassium channel Kv2.1 with the plasma membrane protein components of the exocytotic SNARE complex, syntaxin 1A, and the t-SNARE, syntaxin 1A/SNAP-25, complex. Importantly, the physical interaction of Kv2.1 with syntaxin was shown to be involved in the facilitation of secretion from PC12 cells, which was independent of potassium currents. Recently, we showed that also VAMP2, the vesicular SNARE, interacts physically and functionally with Kv2.1. Here, we first set out to test the interaction of the full SNARE, syntaxin/SNAP-25/VAMP2, complex with the channel. Using the interaction of VAMP2 with Kv2.1 in Xenopus oocytes as a probe, we showed that coexpression of the t-SNARE complex with VAMP2 abolished the VAMP2 effect on channel inactivation and reduced the amount of VAMP2 that coprecipitated with Kv2.1. Further, in vitro pull down assays showed that the full SNARE complex failed to interact with Kv2.1 N- and C-termini in tandem, in contrast to the individual SNARE components. This suggests that the interactions of the SNARE components with Kv2.1 are abolished upon their recruitment into a full SNARE complex, which does not interact with the channel. Other important findings arising from the in vitro study are that the t-SNARE complex, in addition to syntaxin, interacts with a specific C-terminal channel domain, C1a, shown to mediate the facilitation of release by Kv2.1 and that the presence of Kv2.1 N-terminus has crucial contribution to these interactions. These findings provide important insights into the understanding of the complex molecular events involved in the novel phenomenon of secretion facilitation in neuroendocrine cells by Kv2.1.

Effects of a Commercial Supplement of Ophiocordyceps sinensis and Ganoderma lucidum on Physiological Responses to Maximal Exercise in Healthy Young Participants.

Cordyceps sinensis (=Ophiocordyceps sinensis) and Ganoderma lucidum are 2 medicinal mushrooms that have been suggested to have the potential to enhance exercise capacity. We used a commercial supplement combining a traditional Chinese medicine and G. lucidum and tested its effects on human physical, aerobic, and anaerobic capacities. Physical education students (n = 96; 43 women, 53 men; mean ± standard deviation age, 26.3 ± 3.21 years) were randomly divided into 3 groups: low-dose treatment, high-dose treatment, and placebo. Participants received the supplement or the placebo for 28-33 days. Both before and after the intervention, the participants performed a graded maximum oxygen consumption (Vo2max) test on a treadmill and a Wingate anaerobic cycle test (on a different day). The following parameters were measured and recorded during the maximal graded treadmill test: heart rate, oxygen consumption, respiratory exchange ratio, and ventilation. The following parameters were calculated from the Wingate anaerobic cycle test: maximal anaerobic power, mean anaerobic power, and fatigue index. The supplements did not affect Vo2max or the physiological responses upon maximal exercise during the graded treadmill test. In a similar way, they had no effect on peak or mean power, or fatigue index, as measured by the Wingate anaerobic test. A borderline interaction indicated a somewhat lower heart rate at rest after treatment; however, post hoc analysis did not reveal any further statistically significant differences (P = 0.047; F = 3.169). The findings indicate that dual supplementation with C. sinensis and G. lucidum had no effect on Vo2max, on physiological responses at peak exercise load during a graded maximal treadmill test, or on the parameters of anaerobic capacity.

Correction: The effects of a resistance vs. an aerobic single session on attention and executive functioning in adults.

[This corrects the article DOI: 10.1371/journal.pone.0176092.].

The effects of a resistance vs. an aerobic single session on attention and executive functioning in adults.

Evidence from recent studies showed that acute aerobic exercise results in improvements in different cognitive functions. The goal of this study was to assess the influence of acute bouts of aerobic versus resistance exercise on attention and executive function in adults. Thirty-nine physically active adults (age = 52±8 yr) served as participants. Each participant visited the laboratory four times: on the first visit participants performed a cognitive test (NeuroTrax) followed by an aerobic fitness assessment, as well as maximal strength test composed of six exercises. During visits 2-4, participants completed the cognitive test before and after the experimental condition, which consisted of either 25 min of aerobic exercise or resistance exercise, or watching a recorded interview show in a seated position (control condition). Findings indicated significantly higher changes in scores of attention after acute aerobic exercise (mean change 3.46, 95% CI -0.32, 7.27) than following the control condition (mean change -0.64, 95% CI -2.23, 0.96). The changes following resistance exercise (mean change -0.67, 95% CI -4.47, 3.13) were not significantly different from the changes following the control condition. Executive function scores showed a marginally significant improvement following acute aerobic (mean change 4.06, 95% CI 1.68, 6.44) and resistance exercise (mean change 3.69, 95% CI 0.78, 6.60), but not after control (mean change 0.91, 95% CI -1.21, 3.02). We suggest that adults should consider augmenting both modalities into their training routines, which may improve their cognition in addition to providing other physical benefits.

Clinical Effects of a Commercial Supplement of Ophiocordyceps sinensis and Ganoderma lucidum on Cognitive Function of Healthy Young Volunteers.

Ophiocordyceps sinensis (= Cordyceps sinensis) and Ganoderma lucidum are medicinal mushrooms used in traditional Chinese medicine. The effects of O. sinensis and G. lucidum on cognitive function have been evaluated through the use of animal models and in vitro studies, which indicated beneficial effects. The purpose of this study was to evaluate the effects of treatment with a commercially available supplement of O. sinensis and G. lucidum on cognitive function in young, healthy human participants. Physical education students (n = 96 [53 men, 43 women]; mean ± standard deviation age, 26.3 ± 3.21 years) were randomly divided into 3 treatment groups: highdose supplement (HD) group, low-dose supplement (LD) group, and a placebo (PL) group. Each group received the treatment, administered by a technician blinded to supplements/placebo, for 30 days. Participants were evaluated for various cognitive functions before and immediately after treatment. Evaluation of cognitive function domains-global cognitive score, memory, executive function, attention, information processing speed, visuospatial ability, verbal function, and motor skills-showed no significant differences between groups. These results indicate that a combination of O. sinensis and G. lucidum supplements for 30 days did not enhance cognitive function domains in young healthy participants.

Synaptosome-associated protein of 25 kilodaltons modulates Kv2.1 voltage-dependent K(+) channels in neuroendocrine islet beta-cells through an interaction with the channel N terminus.

Insulin secretion is initiated by ionic events involving membrane depolarization and Ca(2+) entry, whereas exocytic SNARE (soluble N-ethylmaleimide-sensitive factor attachment protein receptor) proteins mediate exocytosis itself. In the present study, we characterize the interaction of the SNARE protein SNAP-25 (synaptosome-associated protein of 25 kDa) with the beta-cell voltage-dependent K(+) channel Kv2.1. Expression of Kv2.1, SNAP-25, and syntaxin 1A was detected in human islet lysates by Western blot, and coimmunoprecipitation studies showed that heterologously expressed SNAP-25 and syntaxin 1A associate with Kv2.1. SNAP-25 reduced currents from recombinant Kv2.1 channels by approximately 70% without affecting channel localization. This inhibitory effect could be partially alleviated by codialysis of a Kv2.1N-terminal peptide that can bind in vitro SNAP-25, but not the Kv2.1C-terminal peptide. Similarly, SNAP-25 blocked voltage-dependent outward K(+) currents from rat beta-cells by approximately 40%, an effect that was completely reversed by codialysis of the Kv2.1N fragment. Finally, SNAP-25 had no effect on outward K(+) currents in beta-cells where Kv2.1 channels had been functionally knocked out using a dominant-negative approach, indicating that the interaction is specific to Kv2.1 channels as compared with other beta-cell Kv channels. This study demonstrates that SNAP-25 can regulate Kv2.1 through an interaction at the channel N terminus and supports the hypothesis that SNARE proteins modulate secretion through their involvement in regulation of membrane ion channels in addition to exocytic membrane fusion.

Kv2.1 channel activation and inactivation is influenced by physical interactions of both syntaxin 1A and the syntaxin 1A/soluble N-ethylmaleimide-sensitive factor-25 (t-SNARE) complex with the C terminus of the channel.

Kv2.1, the prevalent delayed-rectifier K(+) channel in neuroendocrine and endocrine cells, was suggested previously by our group to be modulated in islet beta-cells by syntaxin 1A (Syx) and soluble N-ethylmaleimide-sensitive factor attachment protein-25 (SNAP-25). We also demonstrated physical interactions in neuroendocrine cells between Kv2.1, Syx, and SNAP-25, characterized their effects on Kv2.1 activation and inactivation in Xenopus laevis oocytes, and suggested that they pertain to the assembly/disassembly of the Syx/SNAP-25 (t-SNARE) complex. In the present work, we established the existence of a causal relationship between the physical and the functional interactions of Syx with the Kv2.1 channel using three different peptides that compete with the channel for binding of Syx when injected into oocytes already coexpressing Syx with Kv2.1 in the plasma membrane: one peptide corresponding to the Syx-binding region on the N-type Ca(2+) channel, and two peptides corresponding to Syx-binding regions on the Kv2.1 C terminus. All peptides reversed the effects of Syx on Kv2.1, suggesting that the hyperpolarizing shifts of the steady-state inactivation and activation of Kv2.1 caused by Syx result from cell-surface protein-protein interactions and point to participation of the C terminus in such an interaction. In line with these findings, the effects of Syx were dissipated by partial deletions of the C terminus. Furthermore, the t-SNARE complex was shown to bind to the Kv2.1 C terminus, and its effects on the inactivation of Kv2.1 were dissipated by partial deletions of the C terminus. Taken together, these findings suggest that physical interactions of both Syx and the t-SNARE complex with the C terminus of Kv2.1 are involved in channel regulation.

Modulation of a brain voltage-gated K+ channel by syntaxin 1A requires the physical interaction of Gbetagamma with the channel.

Recently we suggested that direct interactions between voltage-gated K(+) channels and proteins of the exocytotic machinery, such as those observed between the Kv1.1/Kvbeta channel, syntaxin 1A, and SNAP-25 may be involved in neurotransmitter release. Furthermore, we demonstrated that the direct interaction with syntaxin 1A enhances the fast inactivation of Kv1.1/Kvbeta1.1 in oocytes. Here we show that G-protein betagamma subunits play a crucial role in the enhancement of inactivation by syntaxin 1A. The effect caused by overexpression of syntaxin 1A is eliminated in the presence of chelators of endogenous betagamma subunits in the whole cell and at the plasma membrane. Conversely, enhancement of inactivation caused by overexpression of beta(1)gamma(2) subunits is eliminated upon knock-down of endogenous syntaxin or its scavenging at the plasma membrane. We further show that the N terminus of Kv1.1 binds brain synaptosomal and recombinant syntaxin 1A and concomitantly binds beta(1)gamma(2); the binding of beta(1)gamma(2) enhances that of syntaxin 1A. Taken together, we suggest a mechanism whereby syntaxin and G protein betagamma subunits interact concomitantly with a Kv channel to regulate its inactivation.

Syntaxin 1A binds to the cytoplasmic C terminus of Kv2.1 to regulate channel gating and trafficking.

Voltage-gated K(+) (Kv) 2.1 is the dominant Kv channel that controls membrane repolarization in rat islet beta-cells and downstream insulin exocytosis. We recently showed that exocytotic SNARE protein SNAP-25 directly binds and modulates rat islet beta-cell Kv 2.1 channel protein at the cytoplasmic N terminus. We now show that SNARE protein syntaxin 1A (Syn-1A) binds and modulates rat islet beta-cell Kv2.1 at its cytoplasmic C terminus (Kv2.1C). In HEK293 cells overexpressing Kv2.1, we observed identical effects of channel inhibition by dialyzed GST-Syn-1A, which could be blocked by Kv2.1C domain proteins (C1: amino acids 412-633, C2: amino acids 634-853), but not the Kv2.1 cytoplasmic N terminus (amino acids 1-182). This was confirmed by direct binding of GST-Syn-1A to the Kv2.1C1 and C2 domains proteins. These findings are in contrast to our recent report showing that Syn-1A binds and modulates the cytoplasmic N terminus of neuronal Kv1.1 and not by its C terminus. Co-expression of Syn-1A in Kv2.1-expressing HEK293 cells inhibited Kv2.1 surfacing, which caused a reduction of Kv2.1 current density. In addition, Syn-1A caused a slowing of Kv2.1 current activation and reduction in the slope factor of steady-state inactivation, but had no affect on inactivation kinetics or voltage dependence of activation. Taken together, SNAP-25 and Syn-1A mediate secretion not only through its participation in the exocytotic SNARE complex, but also by regulating membrane potential and calcium entry through their interaction with Kv and Ca(2+) channels. In contrast to Ca(2+) channels, where these SNARE proteins act on a common synprint site, the SNARE proteins act not only on distinct sites within a Kv channel, but also on distinct sites between different Kv channel families.

Direct interaction of target SNAREs with the Kv2.1 channel. Modal regulation of channel activation and inactivation gating.

Previously we suggested that interaction between voltage-gated K+ channels and protein components of the exocytotic machinery regulated transmitter release. This study concerns the interaction between the Kv2.1 channel, the prevalent delayed rectifier K+ channel in neuroendocrine and endocrine cells, and syntaxin 1A and SNAP-25. We recently showed in islet beta-cells that the Kv2.1 K+ current is modulated by syntaxin 1A and SNAP-25. Here we demonstrate, using co-immunoprecipitation and immunocytochemistry analyses, the existence of a physical interaction in neuroendocrine cells between Kv2.1 and syntaxin 1A. Furthermore, using concomitant co-immunoprecipitation from plasma membranes and two-electrode voltage clamp analyses in Xenopus oocytes combined with in vitro binding analysis, we characterized the effects of these interactions on the Kv2.1 channel gating pertaining to the assembly/disassembly of the syntaxin 1A/SNAP-25 (target (t)-SNARE) complex. Syntaxin 1A alone binds strongly to Kv2.1 and shifts both activation and inactivation to hyperpolarized potentials. SNAP-25 alone binds weakly to Kv2.1 and probably has no effect by itself. Expression of SNAP-25 together with syntaxin 1A results in the formation of t-SNARE complexes, with consequent elimination of the effects of syntaxin 1A alone on both activation and inactivation. Moreover, inactivation is shifted to the opposite direction, toward depolarized potentials, and its extent and rate are attenuated. Based on these results we suggest that exocytosis in neuroendocrine cells is tuned by the dynamic coupling of the Kv2.1 channel gating to the assembly status of the t-SNARE complex.

The 25-kDa synaptosome-associated protein (SNAP-25) binds and inhibits delayed rectifier potassium channels in secretory cells.

Delayed-rectifier K(+) channels (K(DR)) are important regulators of membrane excitability in neurons and neuroendocrine cells. Opening of these voltage-dependent K(+) channels results in membrane repolarization, leading to the closure of the Ca(2+) channels and cessation of insulin secretion in neuroendocrine islet beta cells. Using patch clamp techniques, we have demonstrated that the activity of the K(DR) channel subtype, K(V)1.1, identified by its specific blocker dendrodotoxin-K, is inhibited by SNAP-25 in insulinoma HIT-T15 beta cells. A co-precipitation study of rat brain confirmed that SNAP-25 interacts with the K(V)1.1 protein. Cleavage of SNAP-25 by expression of botulinum neurotoxin A in HIT-T15 cells relieved this SNAP-25-mediated inhibition of K(DR). This inhibitory effect of SNAP-25 is mediated by the N terminus of K(V)1.1, likely by direct interactions with K(Valpha)1.1 and/or K(V)beta subunits, as revealed by co-immunoprecipitation performed in the Xenopus oocyte expression system and in vitro binding. Taken together we have concluded that SNAP-25 mediates secretion not only through its participation in the exocytotic SNARE complex but also by regulating membrane potential and calcium entry through its interaction with K(DR) channels.