Effect of primary, secondary and tertiary amines on membrane potential and intracellular pH in Xenopus laevis oocytes

The effects of primary, secondary and tertiary methyl- and ethylamines as well as of quaternary ammonium compounds on membrane potential, Vm, and intracellular pH (pHi) 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 Vm only slightly. In contrast, primary, secondary and tertiary amines strongly depolarized Vm. Depolarization was inversely proportional to the pKa of the amines. Trimethylamine (pKa 9.8) depolarized Vm 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 Vm 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. pHi 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 Im, decreased from -128 +/- 82 nA (n = 4) at a clamp potential Vc = -70 mV to -3 +/- 33 nA at Vc = 0 mV. Neither delta Vm nor delta Im were markedly inhibited by GdCl3, BaCl2, or amiloride (each 1 mmol/l). Only 1 mmol/l diphenylamine-2-carboxylate (DPC) diminished both responses.(ABSTRACT TRUNCATED AT 250 WORDS)