The relaxation and Ca-pump inhibition in mesenteric artery of normotensive and stroke-prone spontaneously hypertensive rats.

The influences of low temperature and vanadate, both of which have been known to inhibit the Ca-pump activity of membranous systems of smooth muscle cells, on the relaxation of mesenteric artery of stroke-prone spontaneously hypertensive rats (SHRSP) and normotensive Wistar-Kyoto rats (WKY) were studied. Relaxation was induced by the removal of extracellular Ca in high-K-depolarized preparations, so that the involvement of receptor kinetics and changes in membrane potential could be excluded. Relaxation was significantly slower in the preparation from SHRSP than in that from SHRSP. Low temperature prolonged relaxation in preparations from both SHRSP and WKY. No difference in the effect of low temperature was observed between the preparations, which showed Q10 values between 2.8 and 3.5 for 50 and 80% relaxation time. Sodium vanadate also prolonged the time course of relaxation in both preparations. No difference in the effect of sodium vanadate was observed between the preparations from WKY and SHRSP. These results suggest that Ca-pump activity is involved in the relaxation of K-depolarized smooth muscle of mesenteric arteries from both WKY and SHRSP. However, the difference in the pump activity may not contribute greatly to the difference in the relaxation of K-depolarized preparations by the removal of extracellular Ca.