BK channel activation by NS-1619 is partially mediated by intracellular Ca2+ release in smooth muscle cells of porcine coronary artery.
1. Effects of NS-1619, an opener of large conductance Ca2+-activated K+ (BK) channel, on intracellular Ca2+ concentration ([Ca2+]i) and membrane potential were examined in single myocytes freshly isolated from porcine coronary artery. 2. Under current clamp mode, the application of 1-30 microM NS-1619 hyperpolarized the membrane in concentration-dependent manner. The NS-1619-induced hyperpolarization was abolished by the presence of 100 nM iberiotoxin. 3. Application of 1-10 microM NS-1619 hyperpolarized the membrane by approximately 6 mV or less but did not change significantly the [Ca2+]i. When membrane hyperpolarization of 12 mV or so was caused by 30 microM NS-1619, [Ca2+]i was unexpectedly increased by approximately 200 nM. This increase in [Ca2+]i and the concomitant outward current activation were also observed under voltage-clamp at holding potential of -40 mV. 4. The increase in [Ca2+]i by 30 microM NS-1619 occurred mainly in peripheral regions than in the centre of the myocytes. The removal of extracellular Ca2+ affected neither the membrane hyperpolarization nor the increase in [Ca2+]i. 5. In the presence of 10 mM caffeine and 10 microM ryanodine, the increase in [Ca2+]i by 30 microM NS-1619 was not observed and the membrane hyperpolarization was reduced to approximately 67% of the control. 6. These results indicate that the opening of BK channels by NS-1619 at 30 microM, which is the most frequently used concentration of this agent, is partly due to Ca2+ release from caffeine/ryanodine-sensitive intracellular storage sites but is mainly due to the direct activation of the channels.
Yamamura
H
H
Department of Molecular and Cellular Pharmacology, Faculty of Pharmaceutical Sciences, Nagoya City University, Nagoya 467-8603, Japan.
Ohi
Y
Y
Muraki
K
K
Watanabe
M
M
Imaizumi
Y
Y
D000818:Animals; D001562:Benzimidazoles / Q000494:pharmacology*; D002118:Calcium / Q000378:metabolism*; D003331:Coronary Vessels / Q000187:drug effects* / Q000502:physiology; D008564:Membrane Potentials / Q000187:drug effects; D009131:Muscle, Smooth, Vascular / Q000166:cytology / Q000187:drug effects* / Q000502:physiology; D015221:Potassium Channels / Q000187:drug effects* / Q000502:physiology; D013552:Swine
D001562:Benzimidazoles; D015221:Potassium Channels; C086491:NS 1619; D002118:Calcium