[Effect of NH4+ on synaptosomal membrane potential in the rat brain].
The effect of NH4+ on synaptosomal membrane potential was examined using rat brains. The membrane potential was measured by the rhodamine 6G fluorescence method. Both NH4+ diffusion potential (NH4+-potential) and K+ diffusion potential (K+-potential) were observed in the synaptosomes. Upon replacement of medium Cl- with SCN-, both K+- and NH4+-potentials depolarized. On the other hand, replacement of medium Cl- with gluconate resulted in the hyperpolarization of K+-potential, but not of NH4+-potential. Ethacrynic acid (0.3 mM), a Cl- -ATPase inhibitor, depolarized both K+(Cl-)- and NH4+ (Cl-)-potentials. In the presence of ethacrynic acid, both of the potentials were further depolarized by replacement of medium Cl- with SCN-, but not with gluconate-. Picrotoxin (5 mM), a Cl- channel inhibitor, did not significantly affect either K+- or NH4+-potential. In the presence of picrotoxin, replacement of medium Cl- with SCN- depolarized both K+- and NH4+-potentials with or without ethacrynic acid. Gluconate depolarized the K+-potential with ethacrynic acid and the NH4+-potential with or without ethacrynic acid. These findings suggest that NH4+ forms a diffusion potential in nerve endings, and inhibits the anion-mediated hyperpolarization through mechanisms other than anion channels.
Fukunaga
R
R
Department of Biology, Kyoto Pharmaceutical University, Japan.
Simoda
M
M
Ozasa
M
M
Inagaki
C
C
D000641:Ammonia / Q000494:pharmacology* / Q000502:physiology; D000818:Animals; D066298:In Vitro Techniques; D007477:Ions; D008297:Male; D008564:Membrane Potentials / Q000187:drug effects; D010852:Picrotoxin / Q000494:pharmacology; D011188:Potassium / Q000502:physiology; D051381:Rats; D011919:Rats, Inbred Strains; D013574:Synaptosomes / Q000187:drug effects*
D000641:Ammonia; D007477:Ions; D010852:Picrotoxin; D011188:Potassium