Alteration of extracellular calcium dependence in vascular tissue by reserpine

Abstract The extracellular calcium dependence of isolated rabbit aortic strips for contractile responses induced by norepinephrine(NE) and KCl after pretreatment in vivo with reserpine (0.9 mg/kg, i.m; 24 hr) has been investigated. Strips were tested in normal or calcium-free Ringers solution. In normal Ringers, contractile responses of aortae from reserpine-pretreated animals to NE or KCl were significantly potentiated. In calcium-free Ringers, reserpine pretreatment reduced extracellular calcium dependence for contractions induced by NE but increased the extracellular calcium requirement for KCl induced contractions. Higher aortic calcium levels of strips incubated in calcium-free Ringers indicated that reserpine pretreatment significantly increased the affinity of aortic tissue for calcium. After incubation for four hours in calcium-free Ringers, such strips contained 33.5% of control tissue calcium, while only 13.9% of control tissue calcium remained in the normal strips. Thus reserpine pretreatment facilitates the accumulation of a tissue calcium pool and about 21% of this calcium is more firmly bound than normal tissue calcium. These data suggest that the increase in bound calcium is related to the development of supersensitivity and decreased extracellular calcium dependence of NE-induced contractions.