Calcium transport across the basolateral membranes of the enterocyte represents the active step in calcium translocation. This step occurs by two mechanisms, an ATP-dependent pump and a Ca2+/Na+ exchange process. These studies were designed to investigate these two processes in jejunal basolateral membrane vesicles (BLMV) of the spontaneously hypertensive rats (SHR) and their genetically matched controls, Wistar-Kyoto (WKY) rats. The ATP-dependent calcium uptake was stimulated several-fold compared with no ATP condition in both SHR and WKY, but no differences were noted between rate of calcium uptake in SHR and WKY. Kinetics of ATP-dependent calcium uptake at concentrations between 0.01 and 1.0 μM revealed a V max of 0.67 ± 0.03 nmol/mg protein/20 sec and a Km of 0.2 ± 0.03 μM in SHR and V max of 0.69 ± 0.12 and a Km of 0.32 ± 0.14 μM in WKY rats. Ca2+/Na+ exchange in jejunal BLMV of SHR and WKY was investigated in two ways. First, sodium was added to the incubation medium (cis-Na+). Second, Ca2+ efflux from BLMV was studied in the presence of extravesicular Na+ (trans-Na+). Both studies suggest a decreased exchange of calcium and Na+. Kinetic parameters of Na+-dependent Ca2+ uptake at concentrations between 0.01 and 1.0 μM exhibited V max of 0.05 ± 0.01 nanmol/mg protein/5 sec and a Km of 0.21 ± 0.13 μM in SHR and V max of 0.11 ± 0.02 nanmol/mg protein/5 sec and a Km of 0.09 ± 0.05 in WKY, respectively. These results confirm that the intestinal BLMV of SHR and WKY rats have two mechanisms for calcium extrusion, an ATP-dependent Ca2+ transport process and a Na+/Ca2+ exchange process. The ATP-dependent process appears to be functional in SHR; however, the Ca2+/Na+ exchange mechanism appears to have a marked decrease in its maximal capacity. These findings suggest that calcium extrusion via Ca2+/Na+ is impaired in the SHR, which may lead to an increase in intracellular calcium concentration. These findings may have relevance to the development of hypertension.
|Original language||English (US)|
|Number of pages||6|
|Journal||Proceedings of the Society for Experimental Biology and Medicine|
|State||Published - May 1990|
ASJC Scopus subject areas
- Biochemistry, Genetics and Molecular Biology(all)