Involvement of protein kinase C, tyrosine kinases, and Rho kinase in Ca2+ handling of human small arteries

The mechanisms of Ca2+ handling and sensitization were investigated in huma n small omental arteries exposed to norepinephrine (NE) and to the thrombox ane A(2) analog U-46619. Contractions elicited by NE and U-46619 were assoc iated with an increase in intracellular Ca2+ concentration ([Ca2+](i)), an increase in Ca2+ independent signaling pathways, or an enhancement of the s ensitivity of the myofilaments to Ca2+. The two latter pathways were abolis hed by protein kinase C (PKC), tyrosine kinase (TK), and Rho-associated pro tein kinase (ROK) inhibitors. In Ca2+-free medium, both NE and U-46619 elic ited an increase in tension that was greatly reduced by PKC inhibitors and abolished by caffeine or ryanodine. After depletion of Ca2+ stores with NE and U-46619 in Ca2+-free medium, addition of CaCl2 in the continuous presen ce of the agonists produced increases in [Ca2+](i) and contractions that we re inhibited by nitrendipine and TK inhibitors but not affected by PKC inhi bitors. NE and U-46619 induced tyrosine phosphorylation of a 42- or a 58-kD a protein, respectively. These results indicate that the mechanisms leading to contraction elicited by NE and U-46619 in human small omental arteries are composed of Ca2+ release from ryanodine-sensitive stores, Ca2+ influx t hrough nitrendipine-sensitive channels, and Ca2+ sensitization and/or Ca2+- independent pathways. They also show that the TK pathway is involved in the tonic contraction associated with Ca2+ entry, whereas TK, PKC, and ROK mec hanisms regulate Ca2+-independent signaling pathways or Ca2+ sensitization.