AJP - Gastrointestinal and Liver Physiology, Vol 244, Issue 6 618-G622, Copyright © 1983 by American Physiological Society
Mucosal calcium uptake by rat cecum: identity with transcellular calcium absorption
H. N. Nellans and R. S. Goldsmith
Unidirectional intestinal calcium uptake (JCame) at the mucosal surface of
rat cecum was investigated in vitro with intact tissue. Uptake is linear
for 2-3 min with no indication of rapid calcium binding. Kinetic parameters
reveal a maximal velocity of 333 nmol . cm-2 . h-1 with a half-maximal
concentration of 0.98 mM. High-calcium diet decreased JCame by more than
60% with respect to both control and low-calcium diets; 1 mM
N-ethylmaleimide caused a similar reduction. The activation energy of JCame
is significantly less than that of transepithelial mucosal-to-serosal
calcium absorption. Mucosal uptake was compared with transepithelial
calcium fluxes in rat cecum and revealed a 1:1 correlation over a wide
range of transport rates. These results are interpreted to implicate a
feedback control system between basolateral calcium efflux and brush-border
calcium influx.
