PT - JOURNAL ARTICLE AU - Paul H. Ratz AU - Amy S. Miner TI - Role of Protein Kinase Cζ and Calcium Entry in KCl-Induced Vascular Smooth Muscle Calcium Sensitization and Feedback Control of Cellular Calcium Levels AID - 10.1124/jpet.108.142422 DP - 2009 Feb 01 TA - Journal of Pharmacology and Experimental Therapeutics PG - 399--408 VI - 328 IP - 2 4099 - http://jpet.aspetjournals.org/content/328/2/399.short 4100 - http://jpet.aspetjournals.org/content/328/2/399.full SO - J Pharmacol Exp Ther2009 Feb 01; 328 AB - The degree of tonic force (F) maintenance induced in vascular smooth muscle upon K+ depolarization with 110 mM KCl can be greatly reduced by inhibition of rhoA kinase (ROCK). We explored the possibility that a protein kinase C (PKC) isotype may also play a role in causing KCl-induced Ca2+ sensitization. In isometric rings of rabbit artery, the PKC inhibitors, Go-6983 (3-[1-[3-(dimethylamino)propyl]-5-methoxy-1H-indol-3-yl]-4-(1H-indol-3-yl)-1H-pyrrole-2,5-dione), GF-109203X (2-[1-(3-dimethylaminopropyl)indol-3-yl]-3-(indol-3-yl) maleimide), and a cell-permeable (myristoylated) pseudosubstrate inhibitor of PKCζ (PIPKCζ) inhibited KCl-induced tonic F. A myristoylated pseudosubstrate inhibitor of PKCα/β that inhibited phorbol dibutyrate-induced F slightly potentiated KCl-induced tonic F and attenuated 30 mM KCl-induced F. Although the ROCK inhibitor, H-1152 [(S)-(+)-2-methyl-1-[(4-methyl-5-isoquinolinyl)-sulfonyl]-hexahydro-1H-1,4-diazepine dihydrochloride], reduced basal phosphorylation of myosin light-chain phosphatase-targeting subunit at Thr853 (MYPT1-pT853), 3 and 10 μM GF-109203X inhibited only KCl-stimulated phosphorylation, not basal MYPT1-pT853. In fura-2-loaded tissues, GF-109203X and PIPKCζ elevated basal [Ca2+]i (calcium) and potentiated KCl-induced tonic increases in calcium while reducing KCl-induced tonic increases in F. Blockade by nifedipine of Ca2+ entry through voltage-operated Ca2+ channels reduced KCl-induced Ca2+ sensitization and KCl-stimulated but not basal MYPT1-pT853. These data together support a model in which ROCK and PKCζ are constitutively active and function in “resting” muscle to regulate the basal levels of MYPT1-pT853 and calcium, respectively. In this model, KCl-induced increases in calcium activate PKCζ to feed forward and cause additional MYPT1-pT853 above that induced by constitutive ROCK, permitting Ca2+ sensitization and strong F maintenance. Active PKCζ also feeds back to attenuate the degree of KCl-induced increases in calcium. The American Society for Pharmacology and Experimental Therapeutics