Regulation of membrane excitability by intracellular pH (pHi) changers through Ca2+-activated K+ current (BK channel) in single smooth muscle cells from rabbit basilar artery.
Employing microfluorometric system and patch clamp technique in rabbit basilar arterial myocytes, regulation mechanisms of vascular excitability were investigated by applying intracellular pH (pH(i)) changers such as sodium acetate (SA) and NH(4)Cl. Applications of caffeine produced transient phasic contractions in a reversible manner. These caffeine-induced contractions were significantly enhanced by SA and suppressed by NH(4)Cl. Intracellular Ca(2+) concentration ([Ca(2+)](i)) was monitored in a single isolated myocyte and based the ratio of fluorescence using Fura-2 AM (R (340/380)). SA (20 mM) increased and NH(4)Cl (20 mM) decreased R (340/380) by 0.2 +/- 0.03 and 0.1 +/- 0.02, respectively, in a reversible manner. Caffeine (10 mM) transiently increased R (340/380) by 0.9 +/- 0.07, and the ratio increment was significantly enhanced by SA and suppressed by NH(4)Cl, implying that SA and NH(4)Cl may affect [Ca(2+)](i) (p < 0.05). Accordingly, we studied the effects of SA and NH(4)Cl on Ca(2+)-activated K(+) current (IK(Ca)) under patch clamp technique. Caffeine produced transient outward current at holding potential (V (h)) of 0 mV, caffeine induced transient outward K(+) current, and the spontaneous transient outward currents were significantly enhanced by SA and suppressed by NH(4)Cl. In addition, IK(Ca) was significantly increased by acidotic condition when pH(i) was lowered by altering the NH(4)Cl gradient across the cell membrane. Finally, the effects of SA and NH(4)Cl on the membrane excitability and basal tension were studied: Under current clamp mode, resting membrane potential (RMP) was -28 +/- 2.3 mV in a single cell level and was depolarized by 13 +/- 2.4 mV with 2 mM tetraethylammonium (TEA). SA hyperpolarized and NH(4)Cl depolarized RMP by 10 +/- 1.9 and 16 +/- 4.7 mV, respectively. SA-induced hyperpolarization and relaxation of basal tension was significantly inhibited by TEA. These results suggest that SA and NH(4)Cl might regulate vascular tone by altering membrane excitability through modulation of [Ca(2+)](i) and Ca(2+)-activated K channels in rabbit basilar artery.
Park
Jong Kook
JK
Department of Anesthesiology and Pain Medicine, College of Medicine, Cheju National University, 66 Jejudaehakno, Jeju, Jeju Special Self-Governing Province 690-756, South Korea.
Kim
Young Chul
YC
Sim
Jae Hoon
JH
Choi
Mi Young
MY
Choi
Woong
W
Hwang
Kyung-Kuk
KK
Cho
Myeong-Chan
MC
Kim
Ki Whan
KW
Lim
Seung Woon
SW
Lee
Sang Jin
SJ
D000643:Ammonium Chloride / Q000494:pharmacology; D000818:Animals; D001488:Basilar Artery / Q000166:cytology / Q000187:drug effects / Q000502:physiology*; D002110:Caffeine / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism; D002121:Calcium Channel Blockers / Q000494:pharmacology; D020013:Calcium Signaling / Q000187:drug effects; D003593:Cytoplasm / Q000187:drug effects / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D004558:Electric Stimulation; D004594:Electrophysiology; D006863:Hydrogen-Ion Concentration; D007537:Isometric Contraction / Q000187:drug effects; D051036:Large-Conductance Calcium-Activated Potassium Channels / Q000037:antagonists & inhibitors / Q000502:physiology*; D008564:Membrane Potentials / Q000187:drug effects; D032389:Myocytes, Smooth Muscle / Q000166:cytology / Q000187:drug effects / Q000502:physiology*; D009529:Nicardipine / Q000494:pharmacology; D011817:Rabbits; D019346:Sodium Acetate / Q000494:pharmacology; D019789:Tetraethylammonium / Q000494:pharmacology
D002121:Calcium Channel Blockers; D051036:Large-Conductance Calcium-Activated Potassium Channels; D000643:Ammonium Chloride; D002110:Caffeine; D019346:Sodium Acetate; D019789:Tetraethylammonium; D009529:Nicardipine; D002118:Calcium