AJP - Regulatory, Integrative and Comparative Physiology, Vol 244, Issue 3 412-R417, Copyright © 1983 by American Physiological Society
Na+ absorption in Aplysia intestine: Na+ fluxes and intracellular Na+ and K+ activities
G. A. Gerencser
Microelectrodes were used to measure the potential difference (psi m)
across the mucosal membrane of epithelial cells lining the villi of
isolated Aplysia californica intestine. In substrate-free NaCl seawater
medium psi m was -55.1 +/- 1.2 mV. The cell interior was negative relative
to the mucosal bathing solution. Intracellular K+ activity, determined in
the absorptive cells with single-barreled liquid ion-exchanger
microelectrodes, was 383 +/- 15 mM. Since the calculated K+ equilibrium
potential exceeds the membrane potential, K+ is accumulated by the
intestinal absorptive cell. Intracellular Na+ activity (aiNa) was also
determined in the intestinal cells of Aplysia with single-barreled liquid
ion-exchanger microelectrodes and was 17.2 +/- 2.5 mM. aiNa was much less
than that predicted by the electrochemical equilibrium value for Na+ across
the mucosal membrane. From these data the steady-state transapical Na+ and
K+ electrochemical potential differences were calculated. Serosal ouabain
abolished net sodium absorption as determined by flux measurements. These
results are consistent with the operation of a basolateral Na+ - K+ pump.
