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, 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 GdCl3, BaCl2, or amiloride (each 1 mmol/l). 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.