Role of potassium channels in regulation of rat coronary arteriole tone

Activity of potassium (K+) channels plays a key role in regulating arterial tone and therefore blood flow. But little is known about the roles of K+ channels in the coronary arterioles. The aim of the present study was to investigate the influences of several potassium channel blockers on resting vascular tone in isolated rat coronary arteriole. The coronary arterioles were carefully dissected, cannulated and pressurized. The inner diameter of vessels was recorded by a computerized diameter tracking system and the effects of K+ channels on the development of vascular myogenic tone was tested by application of various K+ channel inhibitors. Inhibition of voltage-dependent K+ (KV) channels and inward rectifier K+ (Kir) channels significantly increased the tone constriction. But inhibition of Ca2+-activated K+ (KCa) channels and ATP-sensitive K+ (KATP) channels had no effect on the resting tone. In addition, inhibition of nitric oxide synthase (NOS) further decreased the tone diameter. Combined inhibition of KV, Kir and NOS induced the strongest tone constriction. Our results suggested that activity of KV and Kir channels, and basal nitric oxide (NO) contribute to the myogenic tone in rat coronary arteriole under resting conditions, but basal NO may not contribute to the activation of KV and Kir channels. KCa and KATP channels are likely to have a very low open probability under normal conditions.