Role of smooth muscle cell hyperpolarization in modulation of endothelial cell spontaneous Ca2+ events

Abstract

Smooth muscle cell (SMC) hyperpolarization and consequent vasodilatation has the potential to be associated with increased spontaneous Ca2+ events in endothelial cells (ECs). The underlying mechanisms remain to be determined, but possibilities could include an increased driving force for Ca2+ entry or the presence of hyperpolarization activated channels in the ECs. To hyperpolarize the SMCs, we used 3 μM levcromakalim (LVK) acting at ATP‐sensitive K+ channels (KATP) and 10 mM KCl. Rat cremaster arteries were isolated, double‐cannulated, tied onto glass pipettes (80 mmHg). With a confocal microscope and 40× objective we imaged the ECs loaded with Oregon Green BAPTA‐1 AM to study the intracellular Ca2+ events. LVK and KCl stimulated increased focal spontaneous Ca2+ events, which occasionally propagated as a Ca2+ wave across ECs. These Ca2+ events were significantly decreased following removal of extracellular Ca2+ or application of the KATP channel blocker glibenclamide. These data suggest that LVK and 10 mM KCl evoke increased ECs Ca2+ events, which could have physiological role in the regulation of arterial tone. The work was supported by British Heart Foundation and Wellcome Trust UK.