Cardiovascular diseases (CVD) can induce dysfunction in organ systems by attenuating normal blood flow. Gonadal steroids are vasoactive hormones, but their role in contributing to cardiovascular function remains controversial. We have demonstrated that gonadal steroids can relax coronary arteries by opening the large-conductance, calcium- and voltage-activated potassium (BKca) channel in smooth muscle cells by increasing cyclic nucleotide levels; however, the signaling pathways involved remain to be elucidated. The purpose of this study was to identify how phosphorylation (via cAMP- and cGMP-dependent protein kinases) I dephosphorylation (via phosphoprotein phosphatase 2A, PP2A) regulates BKca channel activity in human coronary artery smooth muscle cells (HCASMC). BKca channel activity was recorded from single HCASMC (Lonza/Clonetics) via single-channel and whole-cell patch-clamp. Channel activity was stimulated by increasing intracellular calcium levels or by increasing either cAMP or cGMP, but the stimulatory effect was mediated predominately via the cGMP-dependent protein kinase. In addition, inhibition of PP2A decreased channel activity. These findings demonstrate that cyclic nucleotide-dependent vasodilators can regulate arterial function via phosphorylation of BKca channels, and that dephosphorylation of the channel (via PP2A) may play a role in channel activation. We propose that modulation of BKca channels via hormone- or drug-induced phosphorylation could be a novel therapeutic means of helping to lower the risk of CVD in both males and females
