TEMPERATURE AND PROTEIN-KINASE-C MODULATE MYOFILAMENT CA2-ARTERIES( SENSITIVITY IN PRESSURIZED RAT CEREBRAL)

The effects of pharmacological activation and inhibition of protein ki nase C (PKC) and temperature on the relationship between cytoplasmic C a2+ and lumen diameter were studied in pressurized (50 mmHg) rat poste rior cerebral arteries permeabilized with alpha-toxin. Increasing Ca2 concentrations (30 nM-10 mu M, 22 degrees C) induced stable, concentr ation-dependent constrictions with a half-maximal effective concentrat ion (EC50) Of 112 nM. The maximal constriction was 80% of baseline dia meter and 157% of that during depolarization of nonpermeabilized vesse ls with 124 mM KCl. Elevation of temperature to 37 degrees C increased the EC50 to 246 nM and enhanced the steepness of concentration-respon se curves. Exposure of permeabilized arteries to indolactam V, an acti vator of PKC, resulted in a significant myofilament Ca2+ sensitization (e.g., EC50 at 5 mu M = 126 nM) without changing efficacy. The effect s of calphostin C, a PKC inhibitor, on Ca2+ sensitivity were minimal; however, the amplitude of Ca2+-induced constrictions in both control a nd indolactam-treated arteries was suppressed in a concentration-depen dent manner. Thus 1) temperature is an important variable in studies o f arterial Ca2+ sensitivity, and 2) changes in PKC activity can signif icantly alter both myofilament sensitivity to and constrictor efficacy of cytosolic Ca2+.