THE ROLE OF CALCIUM IN "NONSPECIFIC" SUPERSENSITIVITY OF VASCULAR MUSCLE

¹ Department of Pharmacology, The University of Texas Medical School at San Antonio, San Antonio, Texas

The development in vascular muscle of supersensitivity to calcium, potassium, acetylcholine, isoproterenol and norepinephrine was studied in rabbit aortic strips after pretreatment with reserpine, either 3 mg/kg 24 hours or 0.3 mg/kg/day for three days before testing. Supersensitivity of the aortae to calcium was obtained in a 60 mM potassium Ringer's solution. Supersensitivity of the aortae to potassium and acetylcholine was obtained only in the presence of calcium. Responses of aortae from reserpine-treated rabbits to isoproterenol and norepinephrine were potentiated both in normal Ringer's solution and in a calcium-free 60 mM potassium Ringer's solution. Aortic strips from reserpinetreated rabbits had a slower rate of tension decline in a calcium-free solution than did the strips from untreated animals. ⁴⁵Ca efflux was delayed after reserpine with a decrease in the rate of the slow component. It is concluded from these results that reserpine increases the permeability of the muscle to calcium and acts in addition at some other calcium site to increase calcium's availability for contraction.