ROLE OF CA2-ACTIVATED K+ CHANNELS IN THE REGULATION OF MEMBRANE-POTENTIAL AND TONE OF SMOOTH-MUSCLE IN HUMAN PIAL-ARTERIES()

Smooth muscle cells (SMCs) in 58% of human pial arteries obtained duri ng surgery showed no spontaneous contractions and displayed a stable r esting membrane potential (MP) of -54.7+/-1.5 mV. Those that exhibited periodic spontaneous contractions associated with periodic depolariza tion and generation of spontaneous action potentials (APs) had a less negative MP of -43.1+/-0.5 mV (42%). Inhibition of calcium-activated p otassium (K-Ca) channels in the silent arteries by charybdotoxin (CTX) and tetraethylammonium ions (TEA) induced dose-dependent depolarizati on, AP generation, and contraction. TEA and CTX enhanced the spontaneo us depolarization and force in arteries that exhibited spontaneous act ivity. They also prolonged the spontaneous APs up to several times and increased their upstroke amplitude. Both TEA and CTX failed to produc e significant depolarization in arteries treated with nifedipine. it i s concluded that K-Ca channels are important regulators of human pial artery SMC resting MP and tone. They are also involved in the control of AP amplitude and duration and the associated contractions. These da ta suggest that alterations in the activity of SMC K-Ca channels could be responsible for the appearance of spontaneous activity in human pi al arteries in vitro and that impaired function of these channels migh t be related to vasospastic phenomena in human cerebral circulation.