Cyclic GMP-dependent Protein Kinase I[alpha] Inhibits Thrombin Receptor-mediated Calcium Mobilization in Vascular Smooth Muscle Cells

Vascular smooth muscle contractile state is regulated by intracellular calcium levels. Nitric oxide causes vascular relaxation by stimulating production of cyclic GMP, which activates type I cGMP-dependent protein kinase (PKGI) in vascular smooth muscle cells (VSMC), inhibiting agonist-induced intracellular Ca²⁺ mobilization ([Ca²⁺][subscript i]). The relative roles of the two PKGI isozymes, PKGI[alpha] and PKGI[beta], in cyclic GMP-mediated inhibition of [Ca²⁺][subscript i] in VSMCs are unclear. Here we have investigated the ability of PKGI isoforms to inhibit [Ca²⁺][subscript i] in response to VSMC activation. Stable Chinese hamster ovary cell lines expressing PKGI[alpha] or PKGI[beta] were created, and the ability of PKGI isoforms to inhibit [Ca²⁺][subscript i] in response to thrombin receptor stimulation was examined. In Chinese hamster ovary cells stably expressing PKGI[alpha] or PKGI[beta], 8-Br-cGMP activation suppressed [Ca²⁺][subscript i] by thrombin receptor activation peptide (TRAP) by 98 ± 1 versus 42 ± 5%, respectively (p