Intracellular acidosis of identified leech neurones produced by substitution of external sodium.
The intracellular pH, pHi, of identified neurones of the central nervous system of the leech Hirudo medicinalis L. was measured with double-barrelled neutral carrier pH-sensitive microelectrodes. The active regulation of pHi of these neurons is due to amiloride-sensitive Na-H exchange and hence requires extracellular Na, Nao. We have measured a decrease of pHi following the removal of Nao. The rate of intracellular acidification in Na-free saline was similar to that in the presence of 2 mM amiloride suggesting that the acidification was due to inhibition of the Na-H exchange. The rate of intracellular acidification depended on the Na substitute chosen; it was 0.02 +/- 0.005 pH units/min (+/- S.D., n = 17) when Na was replaced by N-methyl-D-glucamine. A similar rate of acidification occurred with tris-hydroxymethyl-aminomethane (Tris) while the rate of acidification was higher with bis-2-hydroxymethyl-dimethylammonium (BDA, 0.033 +/- 0.016 pH units/min (+/- S.D., n = 7) and tetramethylammonium (TMA, 0.046 +/- 0.017 pH units/min (n = 3) as Na substitutes. A high, non-linear rate of intracellular acidification was observed, when Li, K or choline were used as Na substitute. The recovery of pHi from acidification upon readdition of Nao was fast, only when Li had replaced Na was the pHi recovery considerably delayed. In conclusion, in all experiments using different Na substitutes the removal of Nao caused a substantial intracellular acidification presumably due to inhibition of Na-H exchange. These changes in pHi might be relevant for results obtained by experiments in which Na-free solutions are used.
Deitmer
J W
JW
Institut für Zoologie I, Universität Düsseldorf, F.R.G.
Schlue
W R
WR
D000818:Animals; D002490:Central Nervous System / Q000187:drug effects / Q000378:metabolism* / Q000502:physiology; D002794:Choline / Q000378:metabolism; D006863:Hydrogen-Ion Concentration; D007865:Leeches / Q000378:metabolism*; D008094:Lithium / Q000378:metabolism; D008536:Meglumine / Q000378:metabolism; D008564:Membrane Potentials / Q000187:drug effects; D009474:Neurons / Q000187:drug effects / Q000378:metabolism* / Q000502:physiology; D012964:Sodium / Q000378:metabolism / Q000502:physiology*
D008536:Meglumine; D008094:Lithium; D012964:Sodium; D002794:Choline