Decreased calcium pump activity in duodenal epithelial cells from spontaneously hypertensive rats

Recently, hypertension research has focused on altered cytosolic free Ca2+, [Ca2+]i, in cells of spontaneously hypertensive rats (SHR). In this work, a mechanism(s) responsible for regulating [Ca2+]i was studied with duodenal epithelial cells isolated from SHR and their control, normotensive Wistar-Kyoto rats (WKY). The equal specific activity of sucrase, an enzyme characteristic of microvilli, in both mucosal scrapings and isolated cells from SHR and WKY suggested that mucosal density of enterocytes was not largely different between the two strains. [Ca2+]i of the isolated cells was estimated with fura-2. Upon incubation in the presence of CaCl2, [Ca2+]i increased to a larger extent in SHR than in WKY cells. Ca2+ efflux based on measurements of [Ca2+]i was decreased in SHR cells. Correspondingly, it was found that 45Ca efflux at 10 sec was lower for SHR cells than for WKY cells. Specific activities of Ca(2+)-stimulated and Ca2+/calmodulin-stimulated ATPases in basolateral plasma membrane preparations were reduced in SHR cells. These results indicated that Ca2+ efflux was decreased by reduction in Ca(2+)-pumping ATPase activity in SHR enterocytes.