Ontogeny of calcium transport by intestinal golgi in spontaneously hypertensive rats and genetically matched WKY rats

Our studies were designed to characterize calcium transport by intestinal Golgi vesicles in spontaneously hypertensive rats (SHR) and their genetically matched control, Wistar-Kyoto rats (WKY). The biochemical purity of the intestinal Golgi in SHR and WKY was validated by marker enzyme studies. Calcium uptake by Golgi vesicles represented transport into the intravesicular space as evidenced by temperature dependency and by calcium ionophore A23187-induced calcium efflux experiments. ATP-driven calcium uptake was stimulated several-fold compared with uptake in the absence of ATP and adenylyl-(β-γ-methylendiphosphate) (nonhydrolyzable ATP) in both SHR and WKY. ATP-dependent calcium uptake was significantly higher in WKY compared with SHR at early times points, 15 s-5 min (p < 0.05-0.01). The initial rate of calcium uptake was linear up to 60 s. Kinetic parameters of calcium uptake at free calcium concentrations of 0.1 to 2.0 μM showed a V_max of 1.64 ± 0.06 and 1.2 ± 0.06 nmol mg protein^-1.15 s^-1 in WKY and SHR, respectively (p < 0.01), and the Km values were 0.17 ± 0.03 and 0.16 ± 0.04 μM, respectively. Kinetic analysis of ATP-dependent calcium uptake in 3-wk-old rats showed a V_max of 0.07 ± 0.005 and 0.36 ± 0.05 nmol/ mg protein^-1.15 s^-1 (p < 0.01) and a Km of 0.26 ± 0.08 and 0.4 ± 0.2 μM in SHR and WKY, respectively. These results suggest that intestinal Golgi vesicles in SHR and WKY demonstrate an ATP-driven calcium uptake. This ATP-dependent process is significantly decreased in the weanling and adult SHR compared with WKY. Such an abnormality in intracellular calcium regulation may have a role in the development of hypertension.