scholarly journals Effects of Intracellular Mg2+ on the Properties of Large-Conductance, Ca2+-Dependent K+ Channels in Rat Cerebrovascular Smooth Muscle Cells

1995 ◽  
Vol 15 (6) ◽  
pp. 1066-1074 ◽  
Author(s):  
Xian Zhang ◽  
Ernest Puil ◽  
David A. Mathers
Keyword(s):  
Smooth Muscle ◽  
Smooth Muscle Cells ◽  
Calcium Ions ◽  
Muscle Cells ◽  
Bk Channels ◽  
Bk Channel ◽  
Voltage Sensitivity ◽  
Open Probability ◽  
Intracellular Magnesium ◽  
Cerebrovascular Smooth Muscle Cells

The effects of intracellular magnesium ions, Mg2+i on large-conductance, Ca2+-dependent K+ channels (BK channels) of adult rat cerebrovascular smooth muscle cells (CVSMCs) were studied using patch clamp techniques and cells enzymatically dispersed from basilar, middle, and posterior cerebral arteries. Recordings used inside-out membrane patches and took place at 20–24°C. One millimeter [Mg2+]i produced a fast block of BK channel currents, as well described by the Woodhull model of channel occlusion by a charged species. However, the affinity and voltage-sensitivity of Mg2+i block were dependent on the concentration of free intracellular calcium ions, [Ca2+]i. Calcium ions may stabilize a channel conformation in which Mg2+i binding sites are relocated closer to the inner membrane surface. In the presence of 1 μ M [Ca2+]i, 0.5 m M [Mg2+]i shifted the Boltzmann curve relating BK channel open probability, Po, to membrane voltage leftward on the voltage axis, without any change in its slope. The enhancing effect of Mg2+i on Po was, therefore, insensitive to membrane potential. Quantitative considerations suggest that physiological levels of Mg2+i tonically facilitate BK channel activation. Alterations of [Mg2+]i during hyper- or hypomagnesemia may contribute to the dilation or contraction of cerebral vessels seen under these two conditions.

scholarly journals Chronic Prenatal Hypoxia Down-Regulated BK Channel Β1 Subunits in Mesenteric Artery Smooth Muscle Cells of the Offspring

2018 ◽  
Vol 45 (4) ◽  
pp. 1603-1616 ◽  
Author(s):  
Bailin Liu ◽  
Yanping Liu ◽  
Ruixiu Shi ◽  
Xueqin Feng ◽  
Xiang Li ◽  
...  
Keyword(s):  
Smooth Muscle ◽  
Smooth Muscle Cells ◽  
Single Channel ◽  
Muscle Cells ◽  
Bk Channels ◽  
Bk Channel ◽  
Mesenteric Arteries ◽  
Prenatal Hypoxia ◽  
Pregnant Rats ◽  
Α Subunit

Background/Aims: Chronic hypoxia in utero could impair vascular functions in the offspring, underlying mechanisms are unclear. This study investigated functional alteration in large-conductance Ca2+-activated K+ (BK) channels in offspring mesenteric arteries following prenatal hypoxia. Methods: Pregnant rats were exposed to normoxic control (21% O2, Con) or hypoxic (10.5% O2, Hy) conditions from gestational day 5 to 21, their 7-month-old adult male offspring were tested for blood pressure, vascular BK channel functions and expression using patch clamp and wire myograh technique, western blotting, and qRT-PCR. Results: Prenatal hypoxia increased pressor responses and vasoconstrictions to phenylephrine in the offspring. Whole-cell currents density of BK channels and amplitude of spontaneous transient outward currents (STOCs), not the frequency, were significantly reduced in Hy vascular myocytes. The sensitivity of BK channels to voltage, Ca2+, and tamoxifen were reduced in Hy myocytes, whereas the number of channels per patch and the single-channel conductance were unchanged. Prenatal hypoxia impaired NS1102- and tamoxifen-mediated relaxation in mesenteric arteries precontracted with phenylephrine in the presence of Nω-nitro-L-arginine methyl ester. The mRNA and protein expression of BK channel β1, not the α-subunit, was decreased in Hy mesenteric arteries. Conclusions: Impaired BK channel β1-subunits in vascular smooth muscle cells contributed to vascular dysfunction in the offspring exposed to prenatal hypoxia.

scholarly journals BK Channels in Rat and Human Pulmonary Smooth Muscle Cells are BKα-β1 Functional Complexes Lacking the Oxygen-Sensitive Stress Axis Regulated Exon Insert

2016 ◽  
Vol 6 (4) ◽  
pp. 563-575 ◽  
Author(s):  
Neil D. Detweiler ◽  
Li Song ◽  
Samantha J. McClenahan ◽  
Rachel J. Versluis ◽  
Sujay V. Kharade ◽  
...  
Keyword(s):  
Smooth Muscle ◽  
Smooth Muscle Cells ◽  
Splice Variants ◽  
Muscle Cells ◽  
Bk Channels ◽  
Bk Channel ◽  
Stress Axis ◽  
Human Donor ◽  
Intracellular Ca ◽  
Oxygen Sensitive

A loss of K+ efflux in pulmonary arterial smooth muscle cells (PASMCs) contributes to abnormal vasoconstriction and PASMC proliferation during pulmonary hypertension (PH). Activation of high-conductance Ca2+-activated (BK) channels represents a therapeutic strategy to restore K+ efflux to the affected PASMCs. However, the properties of BK channels in PASMCs—including sensitivity to BK channel openers (BKCOs)—are poorly defined. The goal of this study was to compare the properties of BK channels between PASMCs of normoxic (N) and chronic hypoxic (CH) rats and then explore key findings in human PASMCs. Polymerase chain reaction results revealed that 94.3% of transcripts encoding BKα pore proteins in PASMCs from N rats represent splice variants lacking the stress axis regulated exon insert, which confers oxygen sensitivity. Subsequent patch-clamp recordings from inside-out (I-O) patches confirmed a dense population of BK channels insensitive to hypoxia. The BK channels were highly activated by intracellular Ca2+ and the BKCO lithocholate; these responses require BK α-β1 subunit coupling. PASMCs of CH rats with established PH exhibited a profound overabundance of the dominant oxygen-insensitive BKα variant. Importantly, human BK (hBK) channels in PASMCs from human donor lungs also represented the oxygen-insensitive BKα variant activated by BKCOs. The hBK channels showed significantly enhanced Ca2+ sensitivity compared with rat BK channels. We conclude that rat BK and hBK channels in PASMCs are oxygen-insensitive BK α-β1 complexes highly sensitive to Ca2+ and the BKCO lithocholate. BK channels are overexpressed in PASMCs of a rat model of PH and may provide an abundant target for BKCOs designed to restore K+ efflux.

ATP activates K and Cl channels via purinoceptor-mediated release of Ca2+ in human coronary artery smooth muscle

1996 ◽  
Vol 271 (5) ◽  
pp. C1463-C1471 ◽  
Author(s):  
D. Strobaek ◽  
P. Christophersen ◽  
S. Dissing ◽  
S. P. Olesen
Keyword(s):  
Smooth Muscle ◽  
Membrane Potential ◽  
Coronary Artery ◽  
Smooth Muscle Cells ◽  
Receptor Agonist ◽  
Muscle Cells ◽  
Receptor Activation ◽  
Bk Channels ◽  
Bk Channel ◽  
Human Coronary Artery

Coronary artery smooth muscle cells express G protein-coupled purinoceptors, and we report here for the first time how receptor activation by extracellular ATP influences cell membrane currents and membrane potential in human cells. ATP (100 microM) stimulated a triphasic change in membrane potential lasting several seconds, which was caused by sequential opening of transient inward and outward conductances. The inward current was carried by Cl- and the outward current by K+, as shown by ion substitution and changes in holding potential. Both currents were independent of the presence of external Ca2+ but were blocked by strong buffering of Ca2+ in the internal solution. The P2u- and P2y-purinoceptor agonists UTP and 2-methylthioadenosine 5'-triphosphate activated similar currents, whereas the P2x-receptor agonist alpha, beta-methyleneadenosine 5'-triphosphate and the P1-receptor agonist adenosine failed to stimulate any whole cell currents. The ATP-activated K+ current was inhibited by iberiotoxin (200 nM), and it was potentiated by the BK channel activator NS-1619 (30 microM). In cell-attached recordings, ATP activated a 230-pS BK channel. In conclusion, ATP acting via P2 purinoceptors stimulated release of Ca2+ from internal stores and transiently activated depolarizing Cl- and hyperpolarizing BK channels in human coronary artery smooth muscle cells.

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.

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.

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