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.