Does calmodulin mediate stimulus-secretion coupling in the parotid gland? Studies using trifluoperazine

Calmodulin present in rat parotid homogenates activated cyclic AMP phosphodiesterase activity by 8 to 10 fold. The activation was Ca2+-dependent and reversed by trifluoperazine. Half-maximal inhibition required 12 microM trifluoperazine. Incubation of parotid slices with up to 40 microM trifluoperazine had no effect on the basal rate of amylase and K+ release or on cellular ATP content. Isoproterenol stimulated glucose utilization and substance P stimulated amylase secretion were also unaffected by 40 microM trifluoperazine. 20 or 40 microM Trifluoperazine however inhibited amylase secretion induced by isoproterenol, dibutyryl cyclic AMP, carbamoylcholine or phenylephrine. The possible involvement of calmodulin in regulating enzyme secretion following stimulation of the parotid gland with the various types of agonists is discussed.