Ionic mechanism for contractile response to hyposmotic challenge in canine basilar arteries

2005 ◽  
Vol 288 (3) ◽  
pp. C702-C709 ◽  
Author(s):  
Shunsuke Yano ◽  
Tomohisa Ishikawa ◽  
Hidetaka Tsuda ◽  
Kazuo Obara ◽  
Koichi Nakayama
Keyword(s):  
Contractile Response ◽  
Reversal Potential ◽  
Ruthenium Red ◽  
Channel Blockers ◽  
Ionic Mechanism ◽  
Pipette Solution ◽  
Voltage Dependent ◽  
Intracellular Ca ◽  
Basilar Arteries ◽  
Canine Basilar Artery

A hyposmotic challenge elicited contraction of isolated canine basilar arteries. The contractile response was nearly abolished by the removal of extracellular Ca2+ and by the voltage-dependent Ca2+ channel (VDCC) blocker nicardipine, but it was unaffected by thapsigargin, which depletes intracellular Ca2+ stores. The contraction was also inhibited by Gd3+ and ruthenium red, cation channel blockers, and Cl− channel blockers DIDS and niflumic acid. The reduction of extracellular Cl− concentrations enhanced the hypotonically induced contraction. Patch-clamp analysis showed that a hyposmotic challenge activated outwardly rectifying whole cell currents in isolated canine basilar artery myocytes. The reversal potential of the current was shifted toward negative potentials by reductions in intracellular Cl− concentration, indicating that the currents were carried by Cl−. Moreover, the currents were abolished by 10 mM BAPTA in the pipette solution and by the removal of extracellular Ca2+. Taken together, these results suggest that a hyposmotic challenge activates cation channels, which presumably cause Ca2+ influx, thereby activating Ca2+-activated Cl− channels. The subsequent membrane depolarization is likely to increase Ca2+ influx through VDCC and elicit contraction.

Ionic mechanisms and Ca2+ regulation in airway smooth muscle contraction: do the data contradict dogma?

2002 ◽  
Vol 282 (6) ◽  
pp. L1161-L1178 ◽  
Author(s):  
Luke J. Janssen
Keyword(s):  
Smooth Muscle ◽  
Airway Smooth Muscle ◽  
Smooth Muscle Contraction ◽  
Channel Blockers ◽  
Excitation Contraction Coupling ◽  
Contraction Coupling ◽  
Spatial And Temporal Heterogeneity ◽  
Voltage Dependent ◽  
Intracellular Ca ◽  
Ionic Mechanisms

In general, excitation-contraction coupling in muscle is dependent on membrane depolarization and hyperpolarization to regulate the opening of voltage-dependent Ca2+ channels and, thereby, influence intracellular Ca2+ concentration ([Ca2+]i). Thus Ca2+ channel blockers and K+ channel openers are important tools in the arsenals against hypertension, stroke, and myocardial infarction, etc. Airway smooth muscle (ASM) also exhibits robust Ca2+, K+, and Cl− currents, and there are elaborate signaling pathways that regulate them. It is easy, then, to presume that these also play a central role in contraction/relaxation of ASM. However, several lines of evidence speak to the contrary. Also, too many researchers in the ASM field view the sarcoplasmic reticulum as being centrally located and displacing its contents uniformly throughout the cell, and they have focused almost exclusively on the initial single [Ca2+] spike evoked by excitatory agonists. Several recent studies have revealed complex spatial and temporal heterogeneity in [Ca2+]i, the significance of which is only just beginning to be appreciated. In this review, we will compare what is known about ion channels in ASM with what is believed to be their roles in ASM physiology. Also, we will examine some novel ionic mechanisms in the context of Ca2+ handling and excitation-contraction coupling in ASM.

Characterizing voltage-dependent Ca2+ channels coupled to VIP release and NO synthesis in enteric synaptosomes

2002 ◽  
Vol 283 (5) ◽  
pp. G1027-G1034 ◽  
Author(s):  
M. Kurjak ◽  
A. Sennefelder ◽  
M. Aigner ◽  
V. Schusdziarra ◽  
H. D. Allescher
Keyword(s):  
Nitric Oxide ◽  
No Synthase ◽  
Channel Blockers ◽  
Voltage Dependent ◽  
Intracellular Ca ◽  
P Type ◽  
Ca2 Channels

In enteric synaptosomes of the rat, the role of voltage-dependent Ca2+channels in K+-induced VIP release and nitric oxide (NO) synthesis was investigated. Basal VIP release was 39 ± 4 pg/mg, and cofactor-substituted NO synthase activity was 7.0 ± 0.8 fmol · mg−1 · min−1. K+ depolarization (65 mM) stimulated VIP release Ca2+ dependently (basal, 100%; K+, 172.2 ± 16.2%; P < 0.05, n = 5). K+-stimulated VIP release was reduced by blockers of the P-type (ω-agatoxin-IVA, 3 × 10−8 M) and N-type (ω-conotoxin-GVIA, 10−6 M) Ca2+ channels by ∼50 and 25%, respectively, but not by blockers of the L-type (isradipine, 10−8 M), Q-type (ω-conotoxin-MVIIC, 10−6 M), or T-type (Ni2+, 10−6 M) Ca2+ channels. In contrast, NO synthesis was suppressed by ω-agatoxin-IVA, ω-conotoxin-GVIA, and isradipine by ∼79, 70, and 70%, respectively, whereas Ni2+ and ω-conotoxin-MVIIC had no effect. These findings are suggestive of a coupling of depolarization-induced VIP release primarily to the P- and N-type Ca2+ channels, whereas NO synthesis is presumably dependent on Ca2+ influx not only via the P- and N- but also via the L-type Ca2+ channel. In contrast, none of the Ca2+ channel blockers affected VIP release evoked by exogenous NO, suggesting that NO induces VIP secretion by a different mechanism, presumably involving intracellular Ca2+ stores.

Ionic mechanism of substance P actions on neurons in trigeminal root ganglia

1990 ◽  
Vol 64 (1) ◽  
pp. 273-281 ◽  
Author(s):  
I. Spigelman ◽  
E. Puil
Keyword(s):  
Substance P ◽  
Voltage Clamp ◽  
Reversal Potential ◽  
Input Resistance ◽  
K Channel ◽  
Resting Membrane Potential ◽  
Channel Blockers ◽  
Ionic Mechanism ◽  
Trigeminal Root

1. Responses of primary sensory neurons to substance P applications by perfusion were studied with intracellular recording techniques in in vitro slice preparations of trigeminal root ganglia (guinea pigs). Application of substance P in micromolar doses produced reversible depolarizations of 2–47 mV in 48 out of 64 neurons. The depolarizing influence facilitated repetitive spike discharge evoked by current-pulse injection. Evidence of desensitization was observed during prolonged or repeated applications of the peptide. 2. The responses to substance P were associated with decreased input resistance, although increased input resistance was observed in neurons where the resting membrane potential was compensated with DC injection. In single-electrode voltage-clamp (SEVC) recordings, substance P evoked an inward shift in the holding current and reduced an outwardly rectifying component in the I-V relationships. The reversal potential for the substance P response could not be determined. These results suggested that the perikaryal response to substance P has a complex ionic mechanism involving activation and deactivation of membrane conductances. 3. Substance P-induced depolarizations were greatly attenuated during perfusion with solutions that were deficient in [Na+] or [Mg2+] and were not significantly affected during perfusion with low-[Ca2+]-, CO2(+)-containing solutions. 4. In the voltage-clamp investigations, an inward current contributed to the substance P responses during combined application with the K(+)-channel blockers, 4-aminopyridine (4-AP) and tetraethylammonium (TEA). This current was not abolished by the inclusion of CsCl in the perfusing solution or by internal Cs+ application from the recording electrode, suggesting that an anomalous inward rectifier was not involved in the responses to substance P.(ABSTRACT TRUNCATED AT 250 WORDS)

Impairment of Ca2+ mobilization in circular muscle cells of the inflamed colon

2000 ◽  
Vol 278 (2) ◽  
pp. G234-G242 ◽  
Author(s):  
Xuan-Zheng Shi ◽  
Sushil K. Sarna
Keyword(s):  
Contractile Response ◽  
Single Cells ◽  
Circular Muscle ◽  
Muscle Cells ◽  
Ruthenium Red ◽  
Cell Length ◽  
Muscle Contractility ◽  
Inositol 1,4,5 Trisphosphate ◽  
Intracellular Ca

This study investigated whether inflammation modulates the mobilization of Ca2+ in canine colonic circular muscle cells. The contractile response of single cells from the inflamed colon was significantly suppressed in response to ACh, KCl, and BAY K8644. Methoxyverapamil and reduction in extracellular Ca2+concentration dose-dependently blocked the response in both normal and inflamed cells. The increase in intracellular Ca2+concentration in response to ACh and KCl was significantly reduced in the inflamed cells. However, Ca2+ efflux from the ryanodine- and inositol 1,4,5-trisphosphate (IP3)-sensitive stores, as well as the decrease of cell length in response to ryanodine and IP3, were not affected. Heparin significantly blocked Ca2+ efflux and contraction in response to ACh in both conditions. ACh-stimulated accumulation of IP3 and the binding of [3H]ryanodine to its receptors were not altered by inflammation. Ruthenium red partially inhibited the response to ACh in normal and inflamed states. We conclude that the canine colonic circular muscle cells utilize Ca2+ influx through L-type channels as well as Ca2+ release from the ryanodine- and IP3-sensitive stores to contract. Inflammation impairs Ca2+ influx through L-type channels, but it may not affect intracellular Ca2+ release. The impairment of Ca2+ influx may contribute to the suppression of circular muscle contractility in the inflamed state.

Mechanical stress-induced Ca2+ entry and Cl− current in cultured human aortic endothelial cells

1999 ◽  
Vol 276 (1) ◽  
pp. C238-C249 ◽  
Author(s):  
Miki Nakao ◽  
Kyoichi Ono ◽  
Susumu Fujisawa ◽  
Toshihiko Iijima
Keyword(s):  
Endothelial Cells ◽  
Reversal Potential ◽  
Ionic Currents ◽  
Induced Current ◽  
Fluid Stream ◽  
Aortic Endothelial Cells ◽  
Voltage Dependent ◽  
Intracellular Ca ◽  
Human Aortic Endothelial Cells ◽  
Aortic Endothelial

A fluid stream through a microtube was applied to cultured human aortic endothelial cells to investigate the endothelial responses of both the ionic currents and intracellular Ca2+concentration ([Ca2+]i) to mechanical stimulation. The fluid stream induced an increase in [Ca2+]ithat was dependent on both the flow rate and the extracellular Ca2+ concentration. Gd3+ and niflumic acid inhibited the fluid stream-induced increase in [Ca2+]i, whereas Ba2+ and tetraethylammonium ion exhibited no effect. The fluid stream-induced [Ca2+]iincrease was accompanied by the activation of an inward current at −52.8 mV. The reversal potential of the fluid stream-induced current shifted to positive potentials when the external Cl− concentration was reduced but was not affected by variation of the external Na+ concentration. During the exposure to the fluid stream, [Ca2+]iwas voltage dependent, i.e., depolarization decreased [Ca2+]i. We therefore conclude that the fluid stream-induced current is largely carried by Cl− and that the Cl− current may thus play a role in modulating the Ca2+ influx by altering the membrane potential of endothelial cells.

scholarly journals Effects of external Rb+ on inward rectifier K+ channels of bovine pulmonary artery endothelial cells.

1994 ◽  
Vol 103 (4) ◽  
pp. 519-548 ◽  
Author(s):  
M R Silver ◽  
M S Shapiro ◽  
T E DeCoursey
Keyword(s):  
Endothelial Cells ◽  
Steady State ◽  
Pulmonary Artery ◽  
Voltage Dependence ◽  
Reversal Potential ◽  
Inward Rectifier ◽  
Partial Substitution ◽  
Pipette Solution ◽  
K Channels ◽  
Voltage Dependent

Inward rectifier (IR) K+ channels of bovine pulmonary artery endothelial cells were studied using the whole-cell, cell-attached, and outside-out patch-clamp configurations. The effects of Rb+ on the voltage dependence and kinetics of IR gating were explored, with [Rb+]o + [K+]o = 160 mM. Partial substitution of Rb+ for K+ resulted in voltage-dependent reduction of inward currents, consistent with Rb+ being a weakly permeant blocker of the IR. In cells studied with a K(+)-free pipette solution, external Rb+ reduced inward IR currents to a similar extent at large negative potentials but block at more positive potentials was enhanced. In outside-out patches, the single-channel i-V relationship was approximately linear in symmetrical K+, but rectified strongly outwardly in high [Rb+]o due to a reduced conductance for inward current. The permeability of Rb+ based on reversal potential, Vrev, was 0.45 that of K+, whereas the Rb+ conductance was much lower, 0.034 that of K+, measured at Vrev-80 mV. The steady state voltage-dependence of IR gating was determined in Rb(+)-containing solutions by applying variable prepulses, followed by a test pulse to a potential at which outward current deactivation was observed. As [Rb+]o was increased, the half-activation potential, V1/2, changed less than Vrev. In high [K+]o solutions V1/2 was Vrev-6 mV, while in high [Rb+]o V1/2 was Vrev + 7 mV. This behavior contrasts with the classical parallel shift of V1/2 with Vrev in K+ solutions. Steady state IR gating was less steeply voltage-dependent in high [Rb+]o than in K+ solutions, with Boltzmann slope factors of 6.4 and 4.4 mV, respectively. Rb+ decreased (slowed) both activation and deactivation rate constants defined at V1/2, and decreased the steepness of the voltage dependence of the activation rate constant by 42%. Deactivation of IR channels in outside-out patches was also slowed by Rb+. In summary, Rb+ can replace K+ in setting the voltage-dependence of IR gating, but in doing so alters the kinetics.

Involvement of stretch-activated cation channels in hypotonically induced insulin secretion in rat pancreatic β-cells

2006 ◽  
Vol 291 (6) ◽  
pp. C1405-C1411 ◽  
Author(s):  
Miki Takii ◽  
Tomohisa Ishikawa ◽  
Hidetaka Tsuda ◽  
Kazumitsu Kanatani ◽  
Takaaki Sunouchi ◽  
...  
Keyword(s):  
Insulin Secretion ◽  
Membrane Depolarization ◽  
Ruthenium Red ◽  
Cell Swelling ◽  
Cation Channels ◽  
Channel Blockers ◽  
Β Cells ◽  
Pancreatic Β Cells ◽  
Voltage Dependent ◽  
Isolated Rat

In isolated rat pancreatic β-cells, hypotonic stimulation elicited an increase in cytosolic Ca2+ concentration ([Ca2+]c) at 2.8 mM glucose. The hypotonically induced [Ca2+]c elevation was significantly suppressed by nicardipine, a voltage-dependent Ca2+ channel blocker, and by Gd3+, amiloride, 2-aminoethoxydiphenylborate, and ruthenium red, all cation channel blockers. In contrast, the [Ca2+]c elevation was not inhibited by suramin, a P2 purinoceptor antagonist. Whole cell patch-clamp analyses showed that hypotonic stimulation induced membrane depolarization of β-cells and produced outwardly rectifying cation currents; Gd3+ inhibited both responses. Hypotonic stimulation also increased insulin secretion from isolated rat islets, and Gd3+ significantly suppressed this secretion. Together, these results suggest that osmotic cell swelling activates cation channels in rat pancreatic β-cells, thereby causing membrane depolarization and subsequent activation of voltage-dependent Ca2+ channels and thus elevating insulin secretion.

Stimulation of voltage-dependent Ca2+ channels by NO at rat myenteric neurons

2007 ◽  
Vol 293 (4) ◽  
pp. G886-G893 ◽  
Author(s):  
Mabruka Sitmo ◽  
Matthias Rehn ◽  
Martin Diener
Keyword(s):  
Enteric Neurons ◽  
Channel Blockers ◽  
No Donor ◽  
Inward Current ◽  
Myenteric Neurons ◽  
Whole Cell Patch Clamp ◽  
Target Organs ◽  
Voltage Dependent ◽  
Intracellular Ca ◽  
Ca2 Channels

The aim of the present study was to characterize the action of the neurotransmitter NO on rat myenteric neurons. A NO donor such as GEA 3162 (10−4 mol/l) induced an increase in the intracellular Ca2+ concentration as indicated by an increase in the fura 2 ratio in ganglia loaded with this Ca2+-sensitive fluorescent dye. The effect of GEA 3162 was strongly reduced in the absence of extracellular Ca2+, suggesting an influx of Ca2+ from the extracellular space evoked by NO. A similar nearly complete inhibition was observed in the presence of Ca2+ channel blockers such as Ni2+ (5 × 10−4 mol/l) or nifedipine (10−6 mol/l). Whole cell patch-clamp recordings confirmed the activation of voltage-dependent Ca2+ channels, measured as inward current carried by Ba2+, by the NO donor. The peak Ba2+-carried inward current increased from −100 ± 19 to −185 ± 34 pA in the presence of sodium nitroprusside (10−4 mol/l). The consequence was a hyperpolarization of the membrane, which was blocked by intracellular Cs+ and thus most probably reflects the activation of Ca2+-dependent K+ channels. Furthermore, at least two subtypes of NO synthases, NOS-1 (neuronal form) and NOS-3 (endothelial form), were found as transcripts in mRNA isolated from the rat myenteric ganglia. The expression of these NO synthases was confirmed immunohistochemically. These observations suggest that NO, released from nitrergic neurons within the enteric nervous system, not only affects target organs such as smooth muscle cells in the gut but has in addition profound effects on the enteric neurons themselves, the key players in the regulation of many gastrointestinal functions.

Inhibition of Anodic Galvanotaxis of Green Paramecia by T-Type Calcium Channel Inhibitors

2007 ◽  
Vol 62 (1-2) ◽  
pp. 93-102 ◽  
Author(s):  
Miki Aonuma ◽  
Takashi Kadono ◽  
Tomonori Kawano
Keyword(s):  
Calcium Channels ◽  
Calcium Channel ◽  
Calcium Ion ◽  
Inhibitory Action ◽  
Regulatory Elements ◽  
Ruthenium Red ◽  
Channel Blockers ◽  
Directed Movement ◽  
Intracellular Ca ◽  
Calcium Channel Inhibitors

Calcium ion (Ca2+) is one of the key regulatory elements for ciliary movements in the Paramecium species. It has long been known that members of Paramecium species including green paramecia (Paramecium bursaria) exhibit galvanotaxis which is the directed movement of cells toward the anode by swimming induced in response to an applied voltage. However, our knowledge on the mode of Ca2+ action during green paramecia anodic galvanotactic response is still largely limited. In the present study, quantification of anodic galvanotaxis was carried out in the presence and absence of various inhibitors of calcium signaling and calcium channels. Interestingly, galvanotactic movement of the cells was completely inhibited by a variety of Ca2+-related inhibitors. Such inhibitors include a Ca2+ chelator (EGTA), general calcium channel blockers (such as lanthanides), inhibitors of intracellular Ca2+ release (such as ruthenium red and neomycin), and inhibitors of T-type calcium channels (such as NNC 55-0396, 1-octanol and Ni2+). However, L-type calcium channel inhibitors such as nimodipine, nifedipine, verapamil, diltiazem and Cd2+ showed no inhibitory action. This may be the first implication for the involvement of T-type calcium channels in protozoan cellular movements.

High-conductance K channels in intercalated cells of the rat distal nephron

2007 ◽  
Vol 292 (3) ◽  
pp. F966-F973 ◽  
Author(s):  
Lawrence G. Palmer ◽  
Gustavo Frindt
Keyword(s):  
Collecting Duct ◽  
Short Circuit ◽  
Reversal Potential ◽  
Bk Channel ◽  
Intercalated Cells ◽  
Cortical Collecting Duct ◽  
High K ◽  
Voltage Dependent ◽  
Intracellular Ca ◽  
High Conductance

High-conductance (BK or maxi) K+ channels were observed in cell-attached patches of the apical membrane of the isolated split-open rat connecting tubule (CNT). These channels were quite rare in cells identified visually as principal cells (PCs; 5/162 patches) but common in intercalated cells (ICs; 24/26 patches). The BK-expressing intercalated cells in the CNT and cortical collecting duct (CCD) were characterized by a low membrane potential (−36 mV) under short-circuit conditions, measured from the reversal potential of the channel currents with similar K+ concentrations on both sides of the membrane. Under whole-cell clamp conditions with low intracellular Ca2+, ICs had a very low K+ conductance. When cell Ca2+ was increased to 200 nM, a voltage-dependent, tetraethylammonium (TEA)-sensitive outward conductance was activated with a limiting value of 90 and 140 nS/cell in the CNT and CCD, respectively. Feeding animals a high-K diet for 1 wk did not increase these currents. TEA-sensitive currents were much smaller in PCs and usually below detection limits. To examine the possibility that the ICs participate in transepithelial K+ secretion, we measured Na/K pump activity as a ouabain-sensitive current. Although these currents were easily observed in PCs, averaging 79 ± 14 and 250 ± 50 pA/cell in the CCD and CNT, respectively, they were below the level of detection in the ICs. We conclude that ICs have BK channel densities that are sufficient to support renal secretion of K+ if cell Ca2+ is elevated. However. a pathway for K+ entry into these cells has not been identified.

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