DIFFERENT CALCIUM STORAGE POOLS IN VASCULAR SMOOTH-MUSCLE CELLS FROM SPONTANEOUSLY HYPERTENSIVE AND NORMOTENSIVE WISTAR-KYOTO RATS

Objective: To evaluate whether the distribution of intracellular free calcium may be impaired in primary hypertension. Design: Cytosolic fre e calcium and stored calcium were investigated in cultured vascular sm ooth muscle cells from spontaneously hypertensive rats (SHR). Methods: The concentrations of intracellular and stored calcium were investiga ted in cultured vascular smooth muscle cells from spontaneously hypert ensive rats aged 6 months from the Munster strain (SHR) and from age-m atched normotensive Wistar-Kyoto (WKY) rats. Vascular smooth muscle ce lls were grown on coverslips, and fluorescence measurements of the int racellular calcium concentration were performed using fura-2. The diff erent effects of thapsigargin, a selective Ca-ATPase inhibitor, and of angiotensin II (Ang II) on the calcium storage pools were investigate d. Results: In the absence of external calcium thapsigargin produced a dose-dependent transient increase in the concentration of intracellul ar calcium in vascular smooth muscle cells. The thapsigargin-induced m aximum peak increase in the concentration of intracellular calcium was not significantly different in SHR and WKY rats. After depletion of t he thapsigargin-sensitive calcium pools the addition of 100 nmol/l Ang II produced a rise in the concentration of intracellular calcium in v ascular smooth muscle cells from SHR and WKY rats. Using vascular smoo th muscle cells from the SHR the Ang II-induced increase in the concen tration of intracellular calcium was not significantly different in th e presence and absence of thapsigargin, indicating that the calcium po ols depleted by thapsigargin and Ang II do not overlap significantly i n vascular smooth muscle cells from SHR. In contrast, in the WKY rats the response to Ang II was significantly diminished after depletion of the thapsigargin-sensitive pool. When Ang II and thapsigargin were ad ministered in the reverse order, i.e. ng II before thapsigargin, the t hapsigargin response was diminished in the WKY rats but not in the SHR . Conclusion: SHR differ from WKY rats in having vascular smooth muscl e cells that contain thapsigargin-sensitive calcium storage pools that are distinct from the Ang It-sensitive calcium pools.