title: Na+ absorption in Aplysia intestine: Na+ fluxes and intracellular Na+ and K+ activities.
abstract: 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.
mesh_terms: D000818:Animals; D001048:Aplysia / Q000378:metabolism*; D007408:Intestinal Absorption / Q000187:drug effects; D007413:Intestinal Mucosa / Q000378:metabolism; D007700:Kinetics; D008839:Microelectrodes; D010042:Ouabain / Q000494:pharmacology; D011188:Potassium / Q000378:metabolism*; D012623:Seawater; D012964:Sodium / Q000378:metabolism*
chemical_list: D010042:Ouabain; D012964:Sodium; D011188:Potassium