NH4+ conductance in Xenopus laevis oocytes. I. Basic observations.
Current-clamp and voltage-clamp techniques were used to study the effects of NH4+ on the cell membrane conductance in Xenopus laevis oocytes. Superfusing the oocytes with NH4Cl resulted in a depolarization of the oocyte's cell membrane potential and, at a clamp potential of -70 mV, in an inward current. The magnitude of the inward current was proportional to the NH4Cl concentration in the extracellular solution and on membrane potential. The reversal potential, Erev , was -35.5 +/- 11.6 mV under control conditions and -3.1 +/- 11.0 mV (n = 19) in the presence 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 shifted the reversal potential to more negative potentials. The NH4Cl-induced current was substantially inhibited by 0.1 mmol/l flufenamate, and was less affected by blockers of the endogenous K+ conductance, Ba2+ and isosorbiddinitrate (ISDN). The results are compatible with the activation of a conductance by NH4Cl for Na+ and NH4+. The mechanism by which NH4Cl activates the conductance remains unknown.
Burckhardt
B C
BC
Zentrum Physiologie und Pathophysiologie, Georg-August-Universität, Humboldtallee 23, D-37073 Göttingen, Germany.
Burckhardt
G
G
D000818:Animals; D000838:Anions; D000894:Anti-Inflammatory Agents, Non-Steroidal / Q000494:pharmacology; D002412:Cations; D004553:Electric Conductivity; D004594:Electrophysiology; D005071:Evoked Potentials; D005260:Female; D005439:Flufenamic Acid / Q000494:pharmacology; D066298:In Vitro Techniques; D007473:Ion Channels / Q000037:antagonists & inhibitors; D017136:Ion Transport / Q000187:drug effects; D008564:Membrane Potentials; D009865:Oocytes / Q000187:drug effects / Q000378:metabolism*; D011188:Potassium / Q000378:metabolism; D000644:Quaternary Ammonium Compounds / Q000378:metabolism*; D012964:Sodium / Q000378:metabolism; D014982:Xenopus laevis
D000838:Anions; D000894:Anti-Inflammatory Agents, Non-Steroidal; D002412:Cations; D007473:Ion Channels; D000644:Quaternary Ammonium Compounds; D005439:Flufenamic Acid; D012964:Sodium; D011188:Potassium