Comparison of inhibitory effects of calcium channel blockers and that of a calmodulin antagonist in strips of mesenteric arteries from spontaneously hypertensive and normotensive rats.

Effects of calcium channel blockers and of calmodulin antagonist on the contractile responses to norepinephrine (NE) were compared between strips of mesenteric arteries from 6- and 14-week-old spontaneously hypertensive rats (SHR) and age-matched, normotensive Wistar-Kyoto rats (WKY). The ratio of the maximum contraction developed by NE to that by 60 mM KCl was significantly increased in strips from 14-week-old SHR. Niludipine, verapamil and diltiazem antagonized the maximum NE contraction to a greater extent in strips from 14-week-old SHR than in those from the WKY. However, the antagonism by niludipine of the KCl- or caffeine-induced contraction was not significantly different between the strips from 14-week-old SHR and those from WKY. In strips from 6-week-old rats, there was no difference in the antagonism by niludipine of the maximum NE contraction. On the other hand, the effect of W-7 on the maximum NE contraction was not significantly different between the strips from 14-week-old SHR and those from WKY. Schild plot analyses demonstrated that alpha 1-adrenoceptors were the same for the strips from SHR and WKY. These results suggest that the enhanced maximum NE contraction in the mesenteric artery from 14-week-old SHR reflects the increased transmembrane influx of calcium, and the activity of calmodulin seems to be the same for the two strains.