scholarly journals Membrane potential and Ca2+ concentration dependence on pressure and vasoactive agents in arterial smooth muscle: A model

2015 ◽  
Vol 146 (1) ◽  
pp. 79-96 ◽  
Author(s):  
Arthur Karlin
Keyword(s):  
Smooth Muscle ◽  
Membrane Potential ◽  
Cerebral Arteries ◽  
Ryanodine Receptors ◽  
Vessel Diameter ◽  
Bk Channels ◽  
Epoxyeicosatrienoic Acid ◽  
Arterial Smooth Muscle ◽  
Cl Channels ◽  
Protein Components

Arterial smooth muscle (SM) cells respond autonomously to changes in intravascular pressure, adjusting tension to maintain vessel diameter. The values of membrane potential (Vm) and sarcoplasmic Ca2+ concentration (Cain) within minutes of a change in pressure are the results of two opposing pathways, both of which use Ca2+ as a signal. This works because the two Ca2+-signaling pathways are confined to distinct microdomains in which the Ca2+ concentrations needed to activate key channels are transiently higher than Cain. A mathematical model of an isolated arterial SM cell is presented that incorporates the two types of microdomains. The first type consists of junctions between cisternae of the peripheral sarcoplasmic reticulum (SR), containing ryanodine receptors (RyRs), and the sarcolemma, containing voltage- and Ca2+-activated K+ (BK) channels. These junctional microdomains promote hyperpolarization, reduced Cain, and relaxation. The second type is postulated to form around stretch-activated nonspecific cation channels and neighboring Ca2+-activated Cl− channels, and promotes the opposite (depolarization, increased Cain, and contraction). The model includes three additional compartments: the sarcoplasm, the central SR lumen, and the peripheral SR lumen. It incorporates 37 protein components. In addition to pressure, the model accommodates inputs of α- and β-adrenergic agonists, ATP, 11,12-epoxyeicosatrienoic acid, and nitric oxide (NO). The parameters of the equations were adjusted to obtain a close fit to reported Vm and Cain as functions of pressure, which have been determined in cerebral arteries. The simulations were insensitive to ±10% changes in most of the parameters. The model also simulated the effects of inhibiting RyR, BK, or voltage-activated Ca2+ channels on Vm and Cain. Deletion of BK β1 subunits is known to increase arterial–SM tension. In the model, deletion of β1 raised Cain at all pressures, and these increases were reversed by NO.

Physiological properties and functions of Ca2+sparks in rat intrapulmonary arterial smooth muscle cells

2002 ◽  
Vol 283 (2) ◽  
pp. L433-L444 ◽  
Author(s):  
Carmelle V. Remillard ◽  
Wei-Min Zhang ◽  
Larissa A. Shimoda ◽  
James S. K. Sham
Keyword(s):  
Smooth Muscle ◽  
Membrane Potential ◽  
Smooth Muscle Cells ◽  
Ryanodine Receptors ◽  
Muscle Cells ◽  
Feedback Mechanism ◽  
Arterial Smooth Muscle ◽  
Endothelin 1 ◽  
Arterial Smooth Muscle Cells ◽  
Specific Regulation

Ca+spark has been implicated as a pivotal feedback mechanism for regulating membrane potential and vasomotor tone in systemic arterial smooth muscle cells (SASMCs), but little is known about its properties in pulmonary arterial smooth muscle cells (PASMCs). Using confocal microscopy, we identified spontaneous Ca2+ sparks in rat intralobar PASMCs and characterized their spatiotemporal properties and physiological functions. Ca2+ sparks of PASMCs had a lower frequency and smaller amplitude than cardiac sparks. They were abolished by inhibition of ryanodine receptors but not by inhibition of inositol trisphosphate receptors and L-type Ca2+ channels. Enhanced Ca2+ influx by BAY K8644, K+, or high Ca2+ caused a significant increase in spark frequency. Functionally, enhancing Ca2+ sparks with caffeine (0.5 mM) caused membrane depolarization in PASMCs, in contrast to hyperpolarization in SASMCs. Norepinephrine and endothelin-1 both caused global elevations in cytosolic Ca2+ concentration ([Ca2+]), but only endothelin-1 increased spark frequency. These results suggest that Ca2+ sparks of PASMCs are similar to those of SASMCs, originate from ryanodine receptors, and are enhanced by Ca2+ influx. However, they play a different modulatory role on membrane potential and are under agonist-specific regulation independent of global [Ca2+].

scholarly journals Opposing roles of smooth muscle BK channels and ryanodine receptors in the regulation of nerve-evoked constriction of mesenteric resistance arteries

2014 ◽  
Vol 306 (7) ◽  
pp. H981-H988 ◽  
Author(s):  
Gayathri Krishnamoorthy ◽  
Swapnil K. Sonkusare ◽  
Thomas J. Heppner ◽  
Mark T. Nelson
Keyword(s):  
Smooth Muscle ◽  
Cerebral Arteries ◽  
Ryanodine Receptors ◽  
Electrical Field Stimulation ◽  
Bk Channels ◽  
Bk Channel ◽  
Mesenteric Arteries ◽  
Resistance Arteries ◽  
Sympathetic Nerve Activation ◽  
Neurogenic Vasoconstriction

In depolarized smooth muscle cells of pressurized cerebral arteries, ryanodine receptors (RyRs) generate “Ca2+ sparks” that activate large-conductance, Ca2+-, and voltage-sensitive potassium (BK) channels to oppose pressure-induced (myogenic) constriction. Here, we show that BK channels and RyRs have opposing roles in the regulation of arterial tone in response to sympathetic nerve activation by electrical field stimulation. Inhibition of BK channels with paxilline increased both myogenic and nerve-induced constrictions of pressurized, resistance-sized mesenteric arteries from mice. Inhibition of RyRs with ryanodine increased myogenic constriction, but it decreased nerve-evoked constriction along with a reduction in the amplitude of nerve-evoked increases in global intracellular Ca2+. In the presence of L-type voltage-dependent Ca2+ channel (VDCC) antagonists, nerve stimulation failed to evoke a change in arterial diameter, and BK channel and RyR inhibitors were without effect, suggesting that nerve- induced constriction is dependent on activation of VDCCs. Collectively, these results indicate that BK channels and RyRs have different roles in the regulation of myogenic versus neurogenic tone: whereas BK channels and RyRs act in concert to oppose myogenic vasoconstriction, BK channels oppose neurogenic vasoconstriction and RyRs augment it. A scheme for neurogenic vasoregulation is proposed in which RyRs act in conjunction with VDCCs to regulate nerve-evoked constriction in mesenteric resistance arteries.

scholarly journals Nanoscale coupling of junctophilin-2 and ryanodine receptors regulates vascular smooth muscle cell contractility

2019 ◽  
Vol 116 (43) ◽  
pp. 21874-21881 ◽  
Author(s):  
Harry A. T. Pritchard ◽  
Caoimhin S. Griffin ◽  
Evan Yamasaki ◽  
Pratish Thakore ◽  
Conor Lane ◽  
...  
Keyword(s):  
Smooth Muscle ◽  
Plasma Membrane ◽  
Cerebral Arteries ◽  
Ryanodine Receptors ◽  
Bk Channels ◽  
Bk Channel ◽  
Functional Coupling ◽  
Superresolution Microscopy ◽  
Cell Contractility ◽  
Channel Currents

Junctophilin proteins maintain close contacts between the endoplasmic/sarcoplasmic reticulum (ER/SR) and the plasma membrane in many types of cells, as typified by junctophilin-2 (JPH2), which is necessary for the formation of the cardiac dyad. Here, we report that JPH2 is the most abundant junctophilin isotype in native smooth muscle cells (SMCs) isolated from cerebral arteries and that acute knockdown diminishes the area of sites of interaction between the SR and plasma membrane. Superresolution microscopy revealed nanometer-scale colocalization of JPH2 clusters with type 2 ryanodine receptor (RyR2) clusters near the cell surface. Knockdown of JPH2 had no effect on the frequency, amplitude, or kinetics of spontaneous Ca2+ sparks generated by transient release of Ca2+ from the SR through RyR2s, but it did nearly abolish Ca2+ spark-activated, large-conductance, Ca2+-activated K+ (BK) channel currents. We also found that JPH2 knockdown was associated with hypercontractility of intact cerebral arteries. We conclude that JPH2 maintains functional coupling between RyR2s and BK channels and is critically important for cerebral arterial function.

β1-subunit of BK channels regulates arterial wall [Ca2+] and diameter in mouse cerebral arteries

2001 ◽  
Vol 91 (3) ◽  
pp. 1350-1354 ◽  
Author(s):  
Matthias Löhn ◽  
Birgit Lauterbach ◽  
Hermann Haller ◽  
Olaf Pongs ◽  
Friedrich C. Luft ◽  
...  
Keyword(s):  
Smooth Muscle ◽  
Smooth Muscle Cells ◽  
Cerebral Arteries ◽  
Muscle Cells ◽  
Bk Channels ◽  
Bk Channel ◽  
Systemic Hypertension ◽  
Myogenic Tone ◽  
Arterial Smooth Muscle ◽  
Arterial Smooth Muscle Cells

Mice with a disrupted β1(BKβ1)-subunit of the large-conductance Ca2+-activated K+ (BK) channel gene develop systemic hypertension and cardiac hypertrophy, which is likely caused by uncoupling of Ca2+ sparks to BK channels in arterial smooth muscle cells. However, little is known about the physiological levels of global intracellular Ca2+ concentration ([Ca2+]i) and its regulation by Ca2+ sparks and BK channel subunits. We utilized a BKβ1 knockout C57BL/6 mouse model and studied the effects of inhibitors of ryanodine receptor and BK channels on the global [Ca2+]i and diameter of small cerebral arteries pressurized to 60 mmHg. Ryanodine (10 μM) or iberiotoxin (100 nM) increased [Ca2+]i by ∼75 nM and constricted +/+ BKβ1 wild-type arteries (pressurized to 60 mmHg) with myogenic tone by ∼10 μm. In contrast, ryanodine (10 μM) or iberiotoxin (100 nM) had no significant effect on [Ca2+]i and diameter of −/− BKβ1-pressurized (60 mmHg) arteries. These results are consistent with the idea that Ca2+ sparks in arterial smooth muscle cells limit myogenic tone through activation of BK channels. The activation of BK channels by Ca2+ sparks reduces the voltage-dependent Ca2+ influx and [Ca2+]i through tonic hyperpolarization. Deletion of BKβ1 disrupts this negative feedback mechanism, leading to increased arterial tone through an increase in global [Ca2+]i.

scholarly journals Large-conductance voltage- and Ca2+-activated K+ channel regulation by protein kinase C in guinea pig urinary bladder smooth muscle

2014 ◽  
Vol 306 (5) ◽  
pp. C460-C470 ◽  
Author(s):  
Kiril L. Hristov ◽  
Amy C. Smith ◽  
Shankar P. Parajuli ◽  
John Malysz ◽  
Georgi V. Petkov
Keyword(s):  
Smooth Muscle ◽  
Membrane Potential ◽  
Guinea Pig ◽  
Bk Channels ◽  
Bk Channel ◽  
K Channel ◽  
Channel Activity ◽  
Open Probability ◽  
Channel Regulation ◽  
Pkc Activation

Large-conductance voltage- and Ca2+-activated K+ (BK) channels are critical regulators of detrusor smooth muscle (DSM) excitability and contractility. PKC modulates the contraction of DSM and BK channel activity in non-DSM cells; however, the cellular mechanism regulating the PKC-BK channel interaction in DSM remains unknown. We provide a novel mechanistic insight into BK channel regulation by PKC in DSM. We used patch-clamp electrophysiology, live-cell Ca2+ imaging, and functional studies of DSM contractility to elucidate BK channel regulation by PKC at cellular and tissue levels. Voltage-clamp experiments showed that pharmacological activation of PKC with PMA inhibited the spontaneous transient BK currents in native freshly isolated guinea pig DSM cells. Current-clamp recordings revealed that PMA significantly depolarized DSM membrane potential and inhibited the spontaneous transient hyperpolarizations in DSM cells. The PMA inhibitory effects on DSM membrane potential were completely abolished by the selective BK channel inhibitor paxilline. Activation of PKC with PMA did not affect the amplitude of the voltage-step-induced whole cell steady-state BK current or the single BK channel open probability (recorded in cell-attached mode) upon inhibition of all major Ca2+ sources for BK channel activation with thapsigargin, ryanodine, and nifedipine. PKC activation with PMA elevated intracellular Ca2+ levels in DSM cells and increased spontaneous phasic and nerve-evoked contractions of DSM isolated strips. Our results support the concept that PKC activation leads to a reduction of BK channel activity in DSM via a Ca2+-dependent mechanism, thus increasing DSM contractility.

Ketamine blocks Ca2+-activated K+ channels in rabbit cerebral arterial smooth muscle cells

2003 ◽  
Vol 285 (3) ◽  
pp. H1347-H1355 ◽  
Author(s):  
Jin Han ◽  
Nari Kim ◽  
Hyun Joo ◽  
Euiyong Kim
Keyword(s):  
Smooth Muscle ◽  
Patch Clamp ◽  
Smooth Muscle Cells ◽  
Cerebral Arteries ◽  
Muscle Cells ◽  
Channel Activity ◽  
Patch Clamp Technique ◽  
Arterial Smooth Muscle ◽  
Clamp Technique ◽  
Arterial Smooth Muscle Cells

Although ketamine and Ca2+-activated K+ (KCa) channels have been implicated in the contractile activity regulation of cerebral arteries, no studies have addressed the specific interactions between ketamine and the KCa channels in cerebral arteries. The purpose of this study was to examine the direct effects of ketamine on KCa channel activities using the patch-clamp technique in single-cell preparations of rabbit middle cerebral arterial smooth muscle. We tested the hypothesis that ketamine modulates the KCa channel activity of the cerebral arterial smooth muscle cells of the rabbit. Vascular myocytes were isolated from rabbit middle cerebral arteries using enzymatic dissociation. Single KCa channel activities of smooth muscle cells from rabbit cerebral arteries were recorded using the patch-clamp technique. In the inside-out patches, ketamine in the micromolar range inhibited channel activity with a half-maximal inhibition of the ketamine conentration value of 83.8 ± 12.9 μM. The Hill coefficient was 1.2 ± 0.3. The slope conductance of the current-voltage relationship was 320.1 ± 2.0 pS between 0 and +60 mV in the presence of ketamine and symmetrical 145 mM K+. Ketamine had little effect on either the voltage-dependency or open- and closed-time histograms of KCa channel. The present study clearly demonstrates that ketamine inhibits KCa channel activities in rabbit middle cerebral arterial smooth muscle cells. This inhibition of KCa channels may represent a mechanism for ketamine-induced cerebral vasoconstriction.

scholarly journals Local Ca2+transients and distribution of BK channels and ryanodine receptors in smooth muscle cells of guinea-pig vas deferens and urinary bladder

2001 ◽  
Vol 534 (2) ◽  
pp. 313-326 ◽  
Author(s):  
Yoshiaki Ohi ◽  
Hisao Yamamura ◽  
Norihiro Nagano ◽  
Susumu Ohya ◽  
Katsuhiko Muraki ◽  
...  
Keyword(s):  
Smooth Muscle ◽  
Urinary Bladder ◽  
Guinea Pig ◽  
Smooth Muscle Cells ◽  
Vas Deferens ◽  
Ryanodine Receptors ◽  
Muscle Cells ◽  
Bk Channels

Ca2+ spark sites in smooth muscle cells are numerous and differ in number of ryanodine receptors, large-conductance K+ channels, and coupling ratio between them

2004 ◽  
Vol 287 (6) ◽  
pp. C1577-C1588 ◽  
Author(s):  
Ronghua ZhuGe ◽  
Kevin E. Fogarty ◽  
Stephen P. Baker ◽  
John G. McCarron ◽  
Richard A. Tuft ◽  
...  
Keyword(s):  
Smooth Muscle ◽  
Smooth Muscle Cells ◽  
High Speed ◽  
Ryanodine Receptors ◽  
Muscle Cells ◽  
Bk Channels ◽  
Wide Field ◽  
Coupling Ratio ◽  
Patch Clamp Recording ◽  
High Speed Imaging

Ca2+ sparks are highly localized Ca2+ transients caused by Ca2+ release from sarcoplasmic reticulum through ryanodine receptors (RyR). In smooth muscle, Ca2+ sparks activate nearby large-conductance, Ca2+-sensitive K+ (BK) channels to generate spontaneous transient outward currents (STOC). The properties of individual sites that give rise to Ca2+ sparks have not been examined systematically. We have characterized individual sites in amphibian gastric smooth muscle cells with simultaneous high-speed imaging of Ca2+ sparks using wide-field digital microscopy and patch-clamp recording of STOC in whole cell mode. We used a signal mass approach to measure the total Ca2+ released at a site and to estimate the Ca2+ current flowing through RyR [ ICa(spark)]. The variance between spark sites was significantly greater than the intrasite variance for the following parameters: Ca2+ signal mass, ICa(spark), STOC amplitude, and 5-ms isochronic STOC amplitude. Sites that failed to generate STOC did so consistently, while those at the remaining sites generated STOC without failure, allowing the sites to be divided into STOC-generating and STOC-less sites. We also determined the average number of spark sites, which was 42/cell at a minimum and more likely on the order of at least 400/cell. We conclude that 1) spark sites differ in the number of RyR, BK channels, and coupling ratio of RyR-BK channels, and 2) there are numerous Ca2+ spark-generating sites in smooth muscle cells. The implications of these findings for the organization of the spark microdomain are explored.

Micromolar Ca2+ from sparks activates Ca2+-sensitive K+ channels in rat cerebral artery smooth muscle

2001 ◽  
Vol 281 (6) ◽  
pp. C1769-C1775 ◽  
Author(s):  
Guillermo J. Pérez ◽  
Adrian D. Bonev ◽  
Mark T. Nelson
Keyword(s):  
Smooth Muscle ◽  
Laser Scanning ◽  
Cerebral Arteries ◽  
Bk Channels ◽  
Bk Channel ◽  
Hill Coefficient ◽  
Channel Activity ◽  
Acetoxymethyl Ester ◽  
Open Probability ◽  
Apparent Dissociation Constant

The goal of the present study was to test the hypothesis that local Ca2+ release events (Ca2+ sparks) deliver high local Ca2+concentration to activate nearby Ca2+-sensitive K+ (BK) channels in the cell membrane of arterial smooth muscle cells. Ca2+ sparks and BK channels were examined in isolated myocytes from rat cerebral arteries with laser scanning confocal microscopy and patch-clamp techniques. BK channels had an apparent dissociation constant for Ca2+ of 19 μM and a Hill coefficient of 2.9 at −40 mV. At near-physiological intracellular Ca2+ concentration ([Ca2+]i; 100 nM) and membrane potential (−40 mV), the open probability of a single BK channel was low (1.2 × 10−6). A Ca2+spark increased BK channel activity to 18. Assuming that 1–100% of the BK channels are activated by a single Ca2+ spark, BK channel activity increases 6 × 105-fold to 6 × 103-fold, which corresponds to ∼30 μM to 4 μM spark Ca2+ concentration. 1,2-bis(2-aminophenoxy)ethane- N,N,N′,N′-tetraacetic acid acetoxymethyl ester caused the disappearance of all Ca2+sparks while leaving the transient BK currents unchanged. Our results support the idea that Ca2+ spark sites are in close proximity to the BK channels and that local [Ca2+]i reaches micromolar levels to activate BK channels.

Sign in / Sign up

Export Citation Format

Share Document