EFFECT OF TREATMENT WITH CHOLECALCIFEROL ON THE MEMBRANE-POTENTIAL AND CONTRACTILITY OF AORTAE FROM SPONTANEOUSLY HYPERTENSIVE RATS

1 The diet of spontaneously hypertensive rats (SHR) and normotensive W istar rats (NWR) was supplemented with 12.5 mu g cholecalciferol per 1 00 g body weight daily, by gavage, for 4 weeks. 2 The amplitude of the contractile responses of aortic rings from SHR to potassium and adren aline, which was smaller than in NWR aortae, was increased after treat ment with cholecalciferol. No further changes were observed in the res ponses of NWR and SHR aortae in the presence of 100 nM apamin. 3 The m embrane potentials of aortae from SHR, which were higher than those of aortae from NWR, decreased after treatment with cholecalciferol. Furt her depolarization was observed in aortic rings from NWR, but not in a ortic rings from SHR, after their preincubation with 100 nM apamin. 4 It is concluded that cholecalciferol normalizes the membrane potential and contractility of aortae from SHR, probably through an effect on l ipid composition and structure of the plasma membrane.