抄録
In order to evaluate the relationship between the calcium-calmodulin system and the adenylate cyclase activity of vascular smooth muscle, we examined the effects of several calcium effectors on the basal and simulated adenylate cyclase activity. Thoracic aortae were removed from Wistar rats and the tissue were homogenated with cold homogenizing buffer containing 1 mM EDTA. Membrane protein fraction of the smooth muscle was prepared by centrifugation at 37, 000g. In this procedure, endogenous guanine nucleotides and contractile proteins remained. The protein fraction was incubated with 2 mM EGTA, 50μM trifluoperazine, 0.1μM A23187 or 25μM calmodulin under basal and stimulated (50 μM isoproterenol, 100μM GTP and 50μM forskolin) conditions. The adenylate cyclase activity was determined by a method modified in our laboratory using double isotope counting. Trifluoperazine reduced the basal adenylate cyclase activity significantly (p < 0.01) as well as the stimulated enzyme activities. A23187 did not affect the basal enzyme activity, but elevated the isoproterenol stimulated enzyme activity significantly (p < 0.02), but did not affect the stimulated enzyme activities. these results suggest that the calcium-calmodulin system is necessary for maintenance of the adenylate cyclase activity of vascular smooth muscle cells. The calmodulin acting site is considered to be the catalytic subunit, and stimulation of the enzyme is accelerated by calcium ion.
