1,25 (OH)2 VITAMIN-D3-INDUCED CA-45 UPTAKE IN VASCULAR MYOCYTES CULTURED FROM SPONTANEOUSLY HYPERTENSIVE AND NORMOTENSIVE RATS

The effect of 1,25 (OH)2 vitamin D3 on basal Ca-45 uptake was examined in vascular smooth muscle cells cultured from mesenteric arteries of spontaneously hypertensive (SHR) and Wistar Kyoto (WKY) normotensive rats. Basal uptake of Ca-45 was significantly greater in myocytes of WKY than SHR at 5, 10, 30 and 60 min incubation with the isotope. Incubation with 1 ng/ml 1,25 (OH)2 vitamin D3 for 48 hr increased basal Ca-45 uptake between 1-10 min in SHR and between 5-10 min in WKY. The dose-response relationship indicated that cells from both strains are equally sensitive to the calciotropic effects of 1,25 (OH)2 vitamin D3 with half-maximal stimulation occurring at approximately 0.3-0.4 ng/ml. In cells of both strains maximal stimulation of Ca-45 uptake was achieved only after a 12-24 hr period of incubation with hormone and pretreatment with cycloheximide inhibited 1,25 (OH)2 vitamin D3-enhanced Ca-45 uptake. Although Ca-45 binding by extracellular matrix material was significantly greater in WKY than SHR, 1,25 (OH)2 vitamin D3 had no effect on the amount of matrix Ca-45 binding in either strain. These results suggest that 1,25 (OH)2 vitamin D3 induces an increase in intracellular protein synthesis that results in enhanced Ca-45 uptake. The similar responses of the two strains indicate that hypertensive smooth muscle is not more sensitive to 1,25 (OH)2 vitamin D3 and the Ca2+ response is a general property of vascular muscle.