Ca2+ antagonist-insensitive coronary smooth muscle contraction involves activation of ε-protein kinase C-dependent pathway

Certain angina and coronary artery disease forms do not respond to Ca2+ channel blockers, and a role for vasoactive eicosanoids such as PGF(2alpha) in Ca2+ antagonist-insensitive coronary vasospasm is suggested; however, the signaling mechanisms are unclear. We investigated whether PGF(2alpha) induced coronary smooth muscle contraction is Ca2+ antagonist insensitive and involves activation of a PKC-dependent pathway. We measured contraction in single porcine coronary artery smooth muscle cells and intracellular free Ca2+ concentration ([Ca2+](i)) in fura 2-loaded cells and examined cytosolic and particulate fractions for PKC activity and reactivity with isoform-specific PKC antibodies. In Hanks' solution (1 mM Ca2+), PGF(2alpha) (10(-5) M) caused transient [Ca2+](i) increase followed by maintained [Ca2+](i) increase and 34% cell contraction. Ca2+ channel blockers verapamil and diltiazem (10(-6) M) abolished maintained PGF(2alpha)-induced [Ca2+](i) increase but only partially inhibited PGF(2alpha)-induced cell contraction to 17%. Verapamil-insensitive PGF(2alpha) contraction was inhibited by PKC inhibitors GF-109203X, calphostin C, and epsilon-PKC V1 -2. PGF(2alpha) caused Ca2+-dependent alpha-PKC and Ca2+-independent epsilon-PKC translocation from cytosolic to particulate fractions that was inhibited by calphostin C. Verapamil abolished PGF(2alpha)- induced alpha- but not epsilon-PKC translocation. PMA (10(-6) M), a direct activator of PKC, caused 21% contraction with no significant [Ca2+](i) increase and epsilon-PKC translocation that were inhibited by calphostin C but not verapamil. Membrane depolarization by 51 mM KCl, which stimulates Ca2+ influx, caused 36% cell contraction and [Ca2+](i) increase that were inhibited by verapamil but not GF-109203X or calphostin C and did not cause alpha- or epsilon-PKC translocation. Thus a significant component of PGF(2alpha)- induced contraction of coronary smooth muscle is Ca2+ antagonist insensitive, involves Ca2+- independent epsilon-PKC activation and translocation, and may represent a signaling mechanism of Ca2+ antagonist-resistant coronary vasospasm.