CALPHOSTIN C-SENSITIVE ENHANCEMENTS OF FORCE BY LYSOPHOSPHATIDYLINOSITOL AND DIACYLGLYCEROLS IN MESENTERIC-ARTERIES FROM THE RAT

1 A pharmacological characterization was made of the effects of lysoph osphatidyl-inositol (lysoPI) and -ethanolamine (lysoPE) on the Ca2+-se nsitivity of contraction in alpha-toxin permeabilized rat mesenteric a rteries. The effect of GTP gamma S (G-protein activator), diacylglycer ols (DAGs, dioctanoyl glycerol (diC(8)) and 1-stearoyl-2-arachidonoyl- sn-glycerol) and phorbol myristate acetate (PMA, protein kinase C (PKC ) activator) on Ca2+-sensitivity was also assessed. 2 LysoPI increased the Ca2+-sensitivity, demonstrated by both an increase in tension ind uced by 1 mu M [Ca2+](free) and an increase in the Ca2+-sensitivity of Ca2+ concentration-tension curves. LysoPE did not enhance force or Ca 2+-sensitivity. 3 GTP gamma S enhanced force at constant Ca2+, increas ed the Ca2+-sensitivity, and increased force under Ca2+-free condition s. PMA also increased force at constant Ca2+ and increased Ca2+-sensit ivity, but caused no force development under Ca2+-free conditions. 4 D AGs, both diC(8) and the more physiological relevant DAG, 1-stearoyl-2 -arachidonoyl-sn-glycerol, enhanced force at constant Ca2+ and increas ed the Ca2+-sensitivity. DiC(8), in contrast to 1-stearoyl-2-arachidon oyl-sn-glycerol, caused force development under Ca2+-free conditions a nd substantially enhanced force at maximal Ca2+-induced contraction. G DP-beta-S abolished the increased Ca2+-sensitization induced by noradr enaline, but not that by DAGs. 5 The PKC inhibitor calphostin C comple tely abolished CA(2+)-sensitization induced by all of the Ca2+-sensiti zing agents. 6 These results show that lysoPI can increase the Ca2+-se nsitivity of smooth muscle contraction, and the Ca2+-sensitization ind uced by DAGs was not completely G-protein mediated, because it was not inhibited by GDP-beta-S. A central role for PKC in regulation of Ca2-sensitization in rat mesenteric small arteries was indicated by the a bolishment of Ca2+-sensitization by calphostin C.