Abstract
1. Smooth muscle cells were isolated from guinea-pig basilar artery and conventional whole-cell recordings of Ca2+ channel activity were made at room temperature within 7 h of the isolation procedure. The purpose of the study was to investigate the mechanism of the stimulatory action of intracellular ATP on Ca2+ channels. 2. High (millimolar) concentrations of ATP were needed to produce stimulation of Ca2+ channels, and neither ADP nor AMP mimicked the action of ATP. 3. The ATP effect was not mimicked by stable ATP derivatives (AMP-PNP or AMP-PCP) and was abolished by incubation of cells in non-specific protein kinase inhibitors (staurosporine or H-7) or specific protein kinase C inhibitors (GF109203x, calphostin C or chelerythrine) but not by tyrosine kinase inhibitors (tyrphostin B42 and genistein). 4. The data suggest that ATP-induced stimulation of L-type Ca2+ channels requires functional activity of a protein kinase C isozyme.