Intracellular K+ activities in Aplysia gut:: Effects of transport inhibitors on the Na+ pump

Na+ absorption by the Aplysia californica foregut is affected through an active Na- transport mechanism located in the basolateral membrane of the epithelial absorptive cells. Since Cl- absorption by the Aplysia gut has been shown to be very different from that demonstrated in vertebrate gut, the present study was undertaken to discern if Na+ transport was also different from that observed in vertebrate preparations. Utilizing microelectrode technique, it was demonstrated that intracellular K+ activity is above electrochemical equilibrium in the Aplysia absorptive cells and that serosal ouabain, Ba2+ or Cd2+-abolished this asymmetry in K- electrochemical potential. Neither bumetanide nor furosemide had any effect on intracellular K- activities, mucosal membrane potentials or transepithelial potentials in the Aplysia gut preparation. These results are consistent with the operation of a basolateral Na+/K+ pump. (C) 1998 Elsevier Science Inc.