Cell Na+ activities and transcellular Na+ absorption by descending colon from normal and Na+-deprived rabbits.
The relation between intracellular Na+ activities, (Na)c, determined employing Na+-selective microelectrodes, and the rates of active Na+ absorption, INa, by rabbit descending colon was examined when INa was varied over a wide range by chronic dietary Na+ deprivation. (Na)c averaged 13 mM and was independent of INa over a sixfold range. Further, the ratios of the slope resistance of the apical membrane (rm) to that of the basolateral membrane (rs) (i.e. rm/rs) in low-transporters (control diet) and high-transporters (Na+-deprived) did not differ significantly inspite of the fact that the Na+ conductance of the apical membranes of high-transporters was, on the average, three times greater than that of the low-transporters. These findings, together with the results reported by other laboratories, strongly suggest that the aldosterone-induced increase in the conductance of the apical membrane to Na+ and, in turn, the rate of entry of Na+ into the absorptive cells are followed by parallel increases in the ability of cells to extrude Na+ across the basolateral membrane in the absence of a sustained increase in (Na)c as well as the conductance of that barrier.
Department of Physiology and Cell Biology, University of Texas, Medical School, Houston 77225.
K
K
Turnheim
R L
RL
Hudson
S G
SG
Schultz
D000818:Animals; D001692:Biological Transport; D002462:Cell Membrane / Q000502:physiology; D003106:Colon / Q000378:metabolism*; D004553:Electric Conductivity; D004848:Epithelium / Q000378:metabolism; D007408:Intestinal Absorption; D008564:Membrane Potentials; D011817:Rabbits; D012964:Sodium / Q000172:deficiency* / Q000378:metabolism
D012964:Sodium