Increased brush-border membrane calcium transport in the intestine, but not the kidney tubule, of spontaneously hypertensive rats.

Abstract

Since we and others have found a decrease in intestinal Ca2+ absorption and renal Ca2+ reabsorption in the mature spontaneously hypertensive rat (SHR) at the tissue and cell level, we asked whether the transport defect was located at the luminal or the basolateral side of the epithelial cell. We studied intestinal and renal Ca2+ transport using isolated epithelial brush-border membrane vesicles (BBMVs) in order to examine the luminal side of this transport. For technical reasons, the preparation of intestinal BBMVs was performed using a centrifugation technique, but for renal BBMVs a precipitation method was used. The vesicles obtained with these two different techniques had markedly different aspects by electron microscopy analysis. However, no morphological difference was apparent between the two rat strains for BBMVs of either preparation. SHR and normotensive control Wistar-Kyoto (WKY) rats were studied at the age of 5 and between 12 and 14 weeks, receiving a normal Ca (1%) and P (0.46%) diet. In 5 week old SHR, duodenal BBMV Ca2+ uptake kinetics were similar to that of WKY of same age. However, in 12 week old rats mean (+/- SD) Vmax of duodenal Ca2+ uptake was significantly enhanced in SHR compared with WKY (0.59 +/- 0.21 v 0.38 +/- 0.09 nmol/mg protein and 10 s, P < .01), whereas Km was similar in the two strains. By contrast, no difference was found for Vmax or Km of Ca2+ uptake in renal BBMVs in 12 week old rats. In conclusion, Ca2+ uptake was either enhanced (duodenum) or normal (kidney tubule) in the mature SHR, compared with the WKY of same age.(ABSTRACT TRUNCATED AT 250 WORDS)