Effects of aspirin and acetic acid on intracellular pH in necturus gastric mucosa.

Intracellular microelectrode techniques were employed to examine the effects of luminal aspirin and acetic acid on intracellular pH and cell membrane potential in the surface epithelial cells of Necturus antrum. Antral mucosa was mounted in a modified Ussing chamber, and intracellular pH was determined from the difference between the potentials recorded by intracellular conventional and pH-sensitive microelectrodes. Under neutral conditions (pH7), aspirin (5 mM) hyperpolarized (-7.5 +/- 1 mV, p less than 0.0001) and acetic acid (5 mM) depolarized (+4 +/- 0.08 mV, p less than 0.001) cell membrane potential. Neither agent had any significant effect on intracellular pH. Under acidic conditions (pH 4.5), aspirin (5 mM) reduced the intracellular pH from 6.99 +/- 0.03 to 6.87 +/- 0.04 (p less than 0.001) and depolarized cell membrane potential from -36.7 +/- 1.5 to -30.3 +/- 1.6 mV, p less than 0.001). Similarly, acetic acid (5 mM) acidified the cells (-0.20 +/- 0.02, p less than 0.001) and depolarized cell membrane potential (+9.6 +/- 1.9 mV, p less than 0.01). These changes suggest that, in the absence of luminal acid, small organic acids, such as aspirin and acetic acid, may have complex effects on the ionic conductances of the surface cell membranes without altering intracellular pH. In contrast, under acidic conditions, these agents increase the permeability of the apical cell membrane-to-acid back-diffusion from the gastric lumen.