Calcium uptake kinetics into brush-border membrane vesicles: Higher Vmax in the spontaneously hypertensive rat than in normotensive control

Abstract

Arterial hypertension in the spontaneously hypertensive rat (SHR) is associated with an abnormal Ca 2+ homeostasis, compared with its normotensive control, the Wistar Kyoto rat (WKY). In particular, epithelial Ca 2+ transport is perturbed, with intestinal absorption and renal tubular reabsorption being decreased in the adolescent and adult SHR. In the present study we examined Ca 2+ uptake into isolated duodenal brush-border membrane vesicles (BBMV) in 12–14 week-old male rats. This uptake can be separated in a non-saturable and a saturable component. The latter follows Michaelis-Menten kinetics. Vmax of this component was found to be significantly higher (p<0.05) in SHR than in WKY (0.58±0.19 versus 0.35±0.06 nmol/mg protein × 10 sec, mean±SD) whereas Km did not differ. Thus, the defect in the intestinal Ca 2+ absorption previously identified in the SHR of this age is not due to a decrease in Ca uptake at the level of the duodenal brush-border membrane, but is most likely located in the baso-lateral membrane.