title: Intestinal calcium transport in spontaneously hypertensive rats (SHR) and their genetically matched WKY rats.
abstract: 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 microM revealed a Vmax of 0.67 +/- 0.03 nmol/mg protein/20 sec and a Km of 0.2 +/- 0.03 microM in SHR and Vmax of 0.69 +/- 0.12 and a Km of 0.32 +/- 0.14 microM 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 microM exhibited Vmax of 0.05 +/- 0.01 nanmol/mg protein/5 sec and a Km of 0.21 +/- 0.13 microM in SHR and Vmax 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.
authors.affiliation: Department of Pediatric Gastroenterology, Vanderbilt University, Nashville, Tennessee 37232.
authors.forename: H
authors.initials: H
authors.lastname: Shibata
authors.forename: F K
authors.initials: FK
authors.lastname: Ghishan
mesh_terms: D000255:Adenosine Triphosphate / Q000494:pharmacology; D000818:Animals; D001692:Biological Transport; D002118:Calcium / Q000378:metabolism*; D005947:Glucose / Q000378:metabolism; D006973:Hypertension / Q000378:metabolism*; D007413:Intestinal Mucosa / Q000378:metabolism*; D051381:Rats; D011918:Rats, Inbred SHR; D011921:Rats, Inbred WKY; D012964:Sodium / Q000378:metabolism
chemical_list: D000255:Adenosine Triphosphate; D012964:Sodium; D005947:Glucose; D002118:Calcium