NH4-LAEVIS OOCYTES .1. BASIC OBSERVATIONS( CONDUCTANCE IN XENOPUS)

Current-clamp and voltage-clamp techniques were used to study the effe cts of NH4+ on the cell membrane conductance in Xenopus laevis oocytes . Superfusing the oocytes with NH,CI resulted in a depolarization of t he oocyte's cell membrane potential curd, at a clamp potential of -70 mV, in an inward current. The magnitude of the inward current was prop ortional to the NH4Cl concentration in the extracellular solution and on membrane potential. The reversal potential, E-rev, was -35.5 +/- 11 .6 mV under control conditions and -3.1 +/- 11.0 mV (n = 19) in the pr esence of NH4Cl (10 mmol/l). Superfusion of the oocytes with nominally Ca2+-free solution affected the NH4Cl-evoked response only marginally . Replacement of extracellular Na+ by N-methyl-D-glucamine(+) markedly reduced, but did not eliminate, the NH4Cl-sensitive current and shift ed the reversal potential to more negative potentials. The NH4Cl-induc ed current was substantially inhibited by 0.1 mmol/l flufenamate, and was less affected by blockers of the endogenous K+ conductance, Ba2+ a nd isosorbiddinitrate (ISDN). The results are compatible with the acti vation of a conductance by NH4Cl for Na+ and NH4+. The mechanism by wh ich NH4Cl activates the conductance remains unknown.