Ontogeny of mitochondrial calcium transport in spontaneously hypertensive (SHR) and WKY rats

The current studies were designed to investigate calcium uptake by intestinal jejunal sacs as well as in intestinal mitochondria of spontaneously hypertensive rats and their genetically matched WKY control rats. Kinetics of jejunal calcium uptake by jejunal sacs of adult SHR and WKY rats showed a significant decrease in V(max) of calcium uptake in SHR (227 ± 24 versus 423 ± 22 nmol.g tissue^-1.3 min^-1) compared to WKY rats P < 0.001. To explore the intracellular handling of calcium by the intestinal mitochondria, calcium uptake was characterized by intestinal mitochondria before (suckling and weanling periods) and after (adult period) development of hypertension. Calcium uptake by intestinal mitochondria was driven by ATP in the presence of succinate as a respiratory substrate. Calcium uptake was stimulated several fold by the presence of ATP compared to no ATP conditions. Maximal calcium uptake occurred between 15-30 min and was significantly greater in adult SHR and WKY rats compared to corresponding values in weanling and suckling rats. Maximal ATP dependent calcium uptake in adult, weanling and suckling WKY rats was significantly greater compared to corresponding mean values in each age group in SHR (P < 0.001). Oligomycin (10 μg/mg protein) inhibited calcium uptake partially. Ruthenium red (0.25 μM), 1 mM sodium azide and 0.5 mM dinitrophenol inhibited calcium uptake by more than 80% in both SHR and WKY rats. Kinetic parameters for ATP stimulated calcium uptake at 10 s revealed a V(max) of 0.56 ± 0.6, 3.46 ± 0.23 and 3.95 ± 0.52 nmol/mg protein/10 s in suckling, weanling and adult WKY rats. These values were significantly greater compared to corresponding mean V(max) values in SHR (0.25 ± 0.02, 0.49 ± 0.08 and 1.4 ± 0.13 nmol/mg protein/10 s P < 0.001). K(m) values for ATP stimulated calcium uptake were not significantly different between SHR and WKY rats. Ca⁺⁺/Na⁺ exchange was also greater in WKY rats compared to SHR. These results confirm previous findings of decreased overall intestinal calcium transport in SHR and shows, for the first time, the presence of abnormality in calcium handling by the intestinal mitochondria of the spontaneously hypertensive rats compared to its genetically matched WKY rats. This abnormality is present before the appearance of hypertension suggesting a genetically determined defect.