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

Abstract

Na + absorption by the Aplysia californica foregut is effected 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 Na + activity is below electrochemical equilibrium in the Aplysia absorptive cells and that amiloride, ouabain, Ba 2+ or Cd 2+ changed this asymmetry in Na + electrochemical potential. Neither bumetanide, furosemide or chlorothiazide had any effect on intracellular Na + 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.