Effects of Dietary Salt on Inhibition of Norepinephrine- Induced Contraction by Ryanodine and Verapamil in Isolated Aortic Rings from Dahl Rats

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Using ryanodine and verapamil, we compared the effects of dietary salt on the relative contribution of sarcoplasmic reticulum (SR) Ca²⁺ release and gated Ca²⁺ entry to arterial contractions induced by norepinephrine (NE) in Dahl salt-sensitive (DS) and salt-resistant (DR) rats. Aortic rings freshly excised from 14DS rats and 13DR rats that had been on low- (0.3%) or high- (8%) NaCl diets for 4 weeks were superfused with physiological saline and isometric tension was measured. The inhibition of the NE (3×10^-8M) -induced contraction of aortic rings by ryanodine (3μM) was significantly greater in DR rats on the low-salt diet than in those on the high-salt diet (p<0.02), but there was no such difference in DS rats. The inhibition of the NE-induced contraction of aortic rings by verapamil (10μM) was significantly greater in DS rats on the high-salt diet than in those on the low-salt diet (p<0.02), but there was no such difference in DR rats. These observations suggest that the effects of dietary salt on gated Ca entry and SR Ca release in NE-induced contraction differ between DS and DR rats. They also suggest that gated Ca²⁺ entry might play an important role in Ca²⁺ control and that the mechanism by which Ca release from SR is reduced might be impaired, or that the ryanodine receptor might be altered in these tissues of salt-fed DS rats. These changes might lead to an elevation of intracellular calcium and contribute to the mechanism of hypertension. (Hypertens Res 1994; 17: 165-171)