Protein kinase C inhibits BK_Ca channel activity in pulmonary arterial smooth muscle

Signaling mechanisms that elevate cyclic AMP (cAMP) activate large-conductance, calcium- and voltage-activated potassium (BK_Ca) channels in pulmonary vascular smooth muscle and cause pulmonary vasodilatation. BK_Ca channel modulation is important in the regulation of pulmonary arterial pressure, and inhibition (closing) of the BK_Ca channel has been implicated in the development of pulmonary vasoconstriction. Protein kinase C (PKC) causes pulmonary vasoconstriction, but little is known about the effect of PKC on BK_Ca channel activity. Accordingly, studies were done to determine the effect of PKC activation on cAMP-induced BK_Ca channel activity using patch-clamp studies in pulmonary arterial smooth muscle cells (PASMC) of the fawn-hooded rat (FHR), a recognized animal model of pulmonary hypertension. Forskolin (10 μM), a stimulator of adenylate cyclase and an activator of cAMP, opened BK_Ca channels in single FHR PASMC, which were blocked by the PKC activators phorbol 12-myristate 13-acetate (100 nM) and thymeleatoxin (100 nM). The inhibitory response by thymeleatoxin on forskolin-induced BK_Ca channel activity was blocked by Gö-6983, which selectively blocks the α, β, δ, γ, and ζ PKC isozymes, and Gö-6976, which selectively inhibits PKC-α, PKC-β, and PKC-μ, but not by rottlerin, which selectively inhibits PKC-δ. Collectively, these results indicate that activation of specific PKC isozymes inhibits cAMP-induced activation of the BK_Ca channel in pulmonary arterial smooth muscle, which suggests a unique signaling pathway to modulate BK_Ca channels and subsequently cAMP-induced pulmonary vasodilatation.