scholarly journals Reduced Ca2+ Spark Activity after Subarachnoid Hemorrhage Disables BK Channel Control of Cerebral Artery Tone

2010 ◽  
Vol 31 (1) ◽  
pp. 3-16 ◽  
Author(s):  
Masayo Koide ◽  
Matthew A Nystoriak ◽  
Gayathri Krishnamoorthy ◽  
Kevin P O'Connor ◽  
Adrian D Bonev ◽  
...  
Keyword(s):  
Subarachnoid Hemorrhage ◽  
Cerebral Artery ◽  
Laser Scanning ◽  
Single Channel ◽  
Cerebral Arteries ◽  
Laser Scanning Confocal Microscopy ◽  
Bk Channels ◽  
Bk Channel ◽  
Channel Activity ◽  
Similar Reduction

Intracellular Ca2+ release events (‘Ca2+ sparks’) and transient activation of large-conductance Ca2+-activated potassium (BK) channels represent an important vasodilator pathway in the cerebral vasculature. Considering the frequent occurrence of cerebral artery constriction after subarachnoid hemorrhage (SAH), our objective was to determine whether Ca2+ spark and BK channel activity were reduced in cerebral artery myocytes from SAH model rabbits. Using laser scanning confocal microscopy, we observed ∼50% reduction in Ca2+ spark activity, reflecting a decrease in the number of functional Ca2+ spark discharge sites. Patch-clamp electrophysiology showed a similar reduction in Ca2+ spark-induced transient BK currents, without change in BK channel density or single-channel properties. Consistent with a reduction in active Ca2+ spark sites, quantitative real-time PCR and western blotting revealed decreased expression of ryanodine receptor type 2 (RyR-2) and increased expression of the RyR-2-stabilizing protein, FKBP12.6, in the cerebral arteries from SAH animals. Furthermore, inhibitors of Ca2+ sparks (ryanodine) or BK channels (paxilline) constricted arteries from control, but not from SAH animals. This study shows that SAH-induced decreased subcellular Ca2+ signaling events disable BK channel activity, leading to cerebral artery constriction. This phenomenon may contribute to decreased cerebral blood flow and poor outcome after aneurysmal SAH.

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.

Peroxynitrite reversibly inhibits Ca2+-activated K+ channels in rat cerebral artery smooth muscle cells

2000 ◽  
Vol 278 (6) ◽  
pp. H1883-H1890 ◽  
Author(s):  
Anna K. Brzezinska ◽  
Debebe Gebremedhin ◽  
William M. Chilian ◽  
Balaraman Kalyanaraman ◽  
Stephen J. Elliott
Keyword(s):  
Single Channel ◽  
Cerebral Arteries ◽  
Ionic Current ◽  
Inhibitory Effect ◽  
Bk Channels ◽  
Bk Channel ◽  
Channel Activity ◽  
Open Probability ◽  
Whole Cell ◽  
Cell Current

Peroxynitrite (ONOO−) is a contractile agonist of rat middle cerebral arteries. To determine the mechanism responsible for this component of ONOO−bioactivity, the present study examined the effect of ONOO− on ionic current and channel activity in rat cerebral arteries. Whole cell recordings of voltage-clamped cells were made under conditions designed to optimize K+ current. The effects of iberiotoxin, a selective inhibitor of large-conductance Ca2+-activated K+ (BK) channels, and ONOO− (10–100 μM) were determined. At a pipette potential of +50 mV, ONOO− inhibited 39% of iberiotoxin-sensitive current. ONOO− was selective for iberiotoxin-sensitive current, whereas decomposed ONOO− had no effect. In excised, inside-out membrane patches, channel activity was recorded using symmetrical K+solutions. Unitary currents were sensitive to increases in internal Ca2+ concentration, consistent with activity due to BK channels. Internal ONOO− dose dependently inhibited channel activity by decreasing open probability and mean open times. The inhibitory effect of ONOO− could be overcome by reduced glutathione. Glutathione, added after ONOO−, restored whole cell current amplitude to control levels and reverted single-channel gating to control behavior. The inhibitory effect of ONOO− on membrane K+ current is consistent with its contractile effects in isolated cerebral arteries and single myocytes. Taken together, our data suggest that ONOO− has the potential to alter cerebral vascular tone by inhibiting BK channel activity.

scholarly journals Differences in Gating Dynamics of BK Channels in Cellular and Mitochondrial Membranes from Human Glioblastoma Cells Unraveled by Short- and Long-Range Correlations Analysis

Cells ◽  
2020 ◽  
Vol 9 (10) ◽  
pp. 2305 ◽  
Author(s):  
Agata Wawrzkiewicz-Jałowiecka ◽  
Paulina Trybek ◽  
Przemysław Borys ◽  
Beata Dworakowska ◽  
Łukasz Machura ◽  
...  
Keyword(s):  
Long Range ◽  
Single Channel ◽  
Cellular Membrane ◽  
Bk Channels ◽  
Bk Channel ◽  
Fluctuation Analysis ◽  
Channel Activity ◽  
Human Glioblastoma ◽  
Long Range Correlations ◽  
Single Channel Activity

The large-conductance voltage- and Ca2+-activated K+ channels (BK) are encoded in humans by the Kcnma1 gene. Nevertheless, BK channel isoforms in different locations can exhibit functional heterogeneity mainly due to the alternative splicing during the Kcnma1 gene transcription. Here, we would like to examine the existence of dynamic diversity of BK channels from the inner mitochondrial and cellular membrane from human glioblastoma (U-87 MG). Not only the standard characteristics of the spontaneous switching between the functional states of the channel is discussed, but we put a special emphasis on the presence and strength of correlations within the signal describing the single-channel activity. The considered short- and long-range memory effects are here analyzed as they can be interpreted in terms of the complexity of the switching mechanism between stable conformational states of the channel. We calculate the dependencies of mean dwell-times of (conducting/non-conducting) states on the duration of the previous state, Hurst exponents by the rescaled range R/S method and detrended fluctuation analysis (DFA), and use the multifractal extension of the DFA (MFDFA) for the series describing single-channel activity. The obtained results unraveled statistically significant diversity in gating machinery between the mitochondrial and cellular BK channels.

Abstract 1368: BK Channel β1 Subunits Are Specific Effectors Of Cholane-induced Channel Activation

Circulation ◽  
2007 ◽  
Vol 116 (suppl_16) ◽  
Author(s):  
Anna Bukiya ◽  
Ligia Toro ◽  
Alejandro M Dopico
Keyword(s):  
Smooth Muscle ◽  
Cerebral Artery ◽  
Vascular Tone ◽  
Lithocholic Acid ◽  
Cerebral Arteries ◽  
Bk Channels ◽  
Bk Channel ◽  
Α Subunit ◽  
Steady State Activity ◽  
Inside Out

The activity of large conductance, Ca 2+ - and voltage-gated potassium (BK) channels in smooth muscle critically controls vascular tone. Depolarization-induced Ca 2+ -entry in the myocyte activates BK channels, which generate outward positive current that tends to repolarize the membrane, limit Ca 2+ entry and, thus, oppose contraction. Cholane-derived steroids (e.g., lithocholic acid, LC) reduce vascular tone in isolated, resistance-size rat cerebral arteries by selective activation of myocyte BK channels. In most tissues, native BK channels consist of pore-forming α (encoded by KCNMA1 or Slo1 ) and accessory β1–4 (encoded by KCNMB1–4 ) subunits. Remarkably, KCNMB expression is tissue-specific: while KCNMB1 is highly predominant in smooth muscle, KCNMB2–4 are not. Thus, agents that target BK β1 subunits may be used to selectively modulate myocyte BK channel function. After cloning the BK α subunit from rat cerebral artery myocytes (termed “cbv1”, AY330293 ), we demonstrated that homomeric cbv1 channel steady-state activity (NPo) was not affected by acute LC application. In contrast, heteromeric cbv1+β1 channel NPo was reversibly increased by LC (+290% of control at EC max ~150 μM; EC 50 =46 μM). Whether the other BK β subunits (2–4) can substitute for β1 to evoke LC-sensitivity in the BK channel remains unknown. To test this, we applied 150 μM LC to the intracellular side of inside-out patches excised from Xenopus laevis oocytes expressing cbv1 alone or cbv1 with a given BK β subunit subtype (1–4). Currents were evoked with the membrane clamped at ±20mV and free Ca 2+ i set to 10 μM, a concentration found in the cerebral artery myocyte during contraction. As previously found, LC consistently failed to increase homomeric cbv1 NPo, while drastically enhancing heteromeric cbv1+β1 channel NPo. Remarkably, LC failed to activate cbv1+β2, cbv1+β3 and cbv1+β4 heteromeric channels. In conclusion, the BK β1 (smooth muscle-type) subunit serves as a unique sensor for cholane-derived steroids. Thus, these compounds provide a platform for designing therapeutic agents to treat cardiovascular disease where reduction of vascular tone is required.

scholarly journals BK Channels Are Activated by Functional Coupling With L-Type Ca2+ Channels in Cricket Myocytes

2021 ◽  
Vol 1 ◽  
Author(s):  
Tomohiro Numata ◽  
Kaori Sato-Numata ◽  
Masami Yoshino
Keyword(s):  
Single Channel ◽  
Bk Channels ◽  
Bk Channel ◽  
Bay K 8644 ◽  
Functional Coupling ◽  
Channel Activity ◽  
Channel Current ◽  
Intracellular Ca ◽  
Patch Clamp Electrophysiology ◽  
Functional Relevance

Large-conductance calcium (Ca2+)-activated potassium (K+) (BK) channel activation is important for feedback control of Ca2+ influx and cell excitability during spontaneous muscle contraction. To characterize endogenously expressed BK channels and evaluate the functional relevance of Ca2+ sources leading to BK activity, patch-clamp electrophysiology was performed on cricket oviduct myocytes to obtain single-channel recordings. The single-channel conductance of BK channels was 120 pS, with increased activity resulting from membrane depolarization or increased intracellular Ca2+ concentration. Extracellular application of tetraethylammonium (TEA) and iberiotoxin (IbTX) suppressed single-channel current amplitude. These results indicate that BK channels are endogenously expressed in cricket oviduct myocytes. Ca2+ release from internal Ca2+ stores and Ca2+ influx via the plasma membrane, which affect BK activity, were investigated. Extracellular Ca2+ removal nullified BK activity. Administration of ryanodine and caffeine reduced BK activity. Administration of L-type Ca2+ channel activity regulators (Bay K 8644 and nifedipine) increased and decreased BK activity, respectively. Finally, the proximity between the L-type Ca2+ channel and BK was investigated. Administration of Bay K 8644 to the microscopic area within the pipette increased BK activity. However, this increase was not observed at a sustained depolarizing potential. These results show that BK channels are endogenously expressed in cricket oviduct myocytes and that BK activity is regulated by L-type Ca2+ channel activity and Ca2+ release from Ca2+ stores. Together, these results show that functional coupling between L-type Ca2+ and BK channels may underlie the molecular basis of spontaneous rhythmic contraction.

scholarly journals Long-term hypoxia increases calcium affinity of BK channels in ovine fetal and adult cerebral artery smooth muscle

2015 ◽  
Vol 308 (7) ◽  
pp. H707-H722 ◽  
Author(s):  
Xiaoxiao Tao ◽  
Mike T. Lin ◽  
Glyne U. Thorington ◽  
Sean M. Wilson ◽  
Lawrence D. Longo ◽  
...  
Keyword(s):  
Flow Cytometry ◽  
Confocal Microscopy ◽  
High Altitude ◽  
Cerebral Artery ◽  
Bk Channels ◽  
Bk Channel ◽  
Channel Activity ◽  
Basilar Arteries ◽  
Near Term

Acclimatization to high-altitude, long-term hypoxia (LTH) reportedly alters cerebral artery contraction-relaxation responses associated with changes in K+ channel activity. We hypothesized that to maintain oxygenation during LTH, basilar arteries (BA) in the ovine adult and near-term fetus would show increased large-conductance Ca2+ activated potassium (BK) channel activity. We measured BK channel activity, expression, and cell surface distribution by use of patch-clamp electrophysiology, flow cytometry, and confocal microscopy, respectively, in myocytes from normoxic control and LTH adult and near-term fetus BA. Electrophysiological data showed that BK channels in LTH myocytes exhibited 1) lowered Ca2+ set points, 2) left-shifted activation voltages, and 3) longer dwell times. BK channels in LTH myocytes also appeared to be more dephosphorylated. These differences collectively make LTH BK channels more sensitive to activation. Studies using flow cytometry showed that the LTH fetus exhibited increased BK β1 subunit surface expression. In addition, in both fetal groups confocal microscopy revealed increased BK channel clustering and colocalization to myocyte lipid rafts. We conclude that increased BK channel activity in LTH BA occurred in association with increased channel affinity for Ca2+ and left-shifted voltage activation. Increased cerebrovascular BK channel activity may be a mechanism by which LTH adult and near-term fetal sheep can acclimatize to long-term high altitude hypoxia. Our findings suggest that increasing BK channel activity in cerebral myocytes may be a therapeutic target to ameliorate the adverse effects of high altitude in adults or of intrauterine hypoxia in the fetus.

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 Regulatory γ1 subunits defy symmetry in functional modulation of BK channels

2018 ◽  
Vol 115 (40) ◽  
pp. 9923-9928 ◽  
Author(s):  
Vivian Gonzalez-Perez ◽  
Manu Ben Johny ◽  
Xiao-Ming Xia ◽  
Christopher J. Lingle
Keyword(s):  
Single Channel ◽  
Regulatory Protein ◽  
Resonance Energy Transfer ◽  
Resonance Energy ◽  
Bk Channels ◽  
Bk Channel ◽  
Single Type ◽  
Regulatory Subunits ◽  
And Function

Structural symmetry is a hallmark of homomeric ion channels. Nonobligatory regulatory proteins can also critically define the precise functional role of such channels. For instance, the pore-forming subunit of the large conductance voltage and calcium-activated potassium (BK, Slo1, or KCa1.1) channels encoded by a single KCa1.1 gene assembles in a fourfold symmetric fashion. Functional diversity arises from two families of regulatory subunits, β and γ, which help define the range of voltages over which BK channels in a given cell are activated, thereby defining physiological roles. A BK channel can contain zero to four β subunits per channel, with each β subunit incrementally influencing channel gating behavior, consistent with symmetry expectations. In contrast, a γ1 subunit (or single type of γ1 subunit complex) produces a functionally all-or-none effect, but the underlying stoichiometry of γ1 assembly and function remains unknown. Here we utilize two distinct and independent methods, a Forster resonance energy transfer-based optical approach and a functional reporter in single-channel recordings, to reveal that a BK channel can contain up to four γ1 subunits, but a single γ1 subunit suffices to induce the full gating shift. This requires that the asymmetric association of a single regulatory protein can act in a highly concerted fashion to allosterically influence conformational equilibria in an otherwise symmetric K+channel.

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.

Detection of Microemboli by Transcranial Doppler Ultrasonography in Aneurysmal Subarachnoid Hemorrhage

Neurosurgery ◽  
2002 ◽  
Vol 50 (5) ◽  
pp. 1026-1031 ◽  
Author(s):  
Jose G. Romano ◽  
Alejandro M. Forteza ◽  
Mauricio Concha ◽  
Sebastian Koch ◽  
Roberto C. Heros ◽  
...  
Keyword(s):  
Subarachnoid Hemorrhage ◽  
Middle Cerebral Artery ◽  
Cerebral Artery ◽  
Transcranial Doppler ◽  
Doppler Ultrasonography ◽  
Aneurysmal Subarachnoid Hemorrhage ◽  
Statistical Significance ◽  
Cerebral Arteries ◽  
Transcranial Doppler Ultrasonography ◽  
Control Subjects

Abstract OBJECTIVE: To determine the frequency and characteristics of microembolic signals (MES) in subarachnoid hemorrhage (SAH). METHODS: Twenty-three patients with aneurysmal SAH were monitored with transcranial Doppler ultrasonography for the presence of MES and vasospasm. Each middle cerebral artery was monitored for 30 minutes three times each week. Patients were excluded if they had traumatic SAH or cardiac or arterial sources of emboli. Monitoring was initiated 6.3 days (1–16 d) after SAH and lasted 6.6 days (1–13 d). Eleven individuals without SAH or other cerebrovascular diseases who were treated in the same unit served as control subjects. Each patient underwent monitoring of both middle cerebral arteries a mean of three times; therefore, 46 vessels were studied (a total of 138 observations). Control subjects underwent assessment of each middle cerebral artery once, for a total of 22 control vessels. RESULTS: MES were detected for 16 of 23 patients (70%) and 44 of 138 patient vessels (32%) monitored, compared with 2 of 11 control subjects (18%) and 2 of 22 control vessels (9%) (P < 0.05). MES were observed for 83% of patients with clinical vasospasm and 54% of those without clinical vasospasm. Ultrasonographic vasospasm was observed for 71 of 138 vessels monitored; MES were observed for 28% of vessels with vasospasm and 36% of those without vasospasm. Aneurysms proximal to the monitored artery were identified in 38 of 138 vessels, of which 34% exhibited MES, which is similar to the frequency for vessels without proximal aneurysms (31%). Coiled, clipped, and unsecured aneurysms exhibited similar frequencies of MES. CONCLUSION: MES were common in SAH, occurring in 70% of cases of SAH and one-third of all vessels monitored. Although MES were more frequent among patients with clinical vasospasm, this difference did not reach statistical significance. We were unable to demonstrate a relationship between ultrasonographic vasospasm and MES, and the presence of a proximal secured or unsecured aneurysm did not alter the chance of detection of MES. Further studies are required to determine the origin and clinical relevance of MES in SAH.

Sign in / Sign up

Export Citation Format

Share Document