Effect of primary, secondary and tertiary amines on membrane potential and intracellular pH in Xenopus laevis oocytes
Burckhardt, B.C.; Thelen, P.
Pflugers Archiv European Journal of Physiology 429(3): 306-312
1995
ISSN/ISBN: 0031-6768 PMID: 7761254 Document Number: 443169
The effects of primary, secondary and tertiary methyl- and ethylamines as well as of quaternary ammonium compounds on membrane potential, V-m, and intracellular pH (pH-i) of oocytes from Xenopus laevis were studied using electrophysiological methods. The quaternary ammonium compounds, tetramethyl- (TMA) and tetraethyl- (TEA) ammonium chloride and choline chloride (each 10 mmol/l), affected V-m only slightly. In contrast, primary, secondary and tertiary amines strongly depolarized V-m. Depolarization was inversely proportional to the pK-a of the amines. Trimethylamine (pK-a 9.8) depolarized V-m by 61.7 +- 21.8 mV (n=13) and exerted its half-maximal effect at less than 2 mmol/l. In paired experiments (n=6), trimethylamine (10 mmol/l) reduced V-m only by 5.1+-1.3 mV at a bath pH of 6.0, but by 73.2+-20.0 mV at pH 7.5, suggesting that the deprotonated, uncharged form of the amines was responsible for the depolarization. pH-i measurements using the Fluka pH-sensitive cocktail 95 293 revealed a short initial alkalinization and a subsequent acidification in the presence of trimethylamine (10 mmol/l). The intracellular acidification proceeded much more slowly than the depolarization. As shown by measurements using a two-electrode voltage-clamp device, the depolarization was associated with an inward current. This trimethylamine-sensitive current, DELTA-I-m, decreased from -128+-82 nA (n=4) at a clamp potential V-c=-70 mV to -3+-33 nA at V-c=0 mV. Neither DELTA-V-m nor DELTA-I-m were markedly inhibited by GdCl-3, BaCl-2, or amiloride (each 1 mmol/1). Only 1 mmol/l diphenylamine-2-carboxylate (DPC) diminished both responses. The data suggest that the amines modify anion or cation conductances of the oocytes by as yet unknown mechanisms.