THE EFFECTS OF L-ALANINE AND ACETYLCHOLINE ON MEMBRANE POTENTIAL, ⁴⁵Ca²⁺ AND ⁸⁶Rb⁺ EFFLUX AND AMYLASE SECRETION IN THE ISOLATED MOUSE PANCREAS

¹ Medical Research Council Secretory Control Group, The Physiological Laboratory, University of Liverpool, P.O. Box 147, Liverpool L69 3BX

A comparative study was made of the effects of acetylcholine (ACh) and the neutral amino acid L-alanine on membrane potential, ⁴⁵Ca²⁺ and ⁸⁶Rb⁺ fractional efflux, and amylase secretion in segments of the isolated mouse pancreas. Both ACh and L-alanine evoked similar dose-dependent depolarizations of pancreatic acinar cells. ACh, but not L-alanine, caused a marked reduction in input resistance and evoked electrical uncoupling of acinar cells at high concentrations. Measurements of ⁴⁵Ca²⁺ release from pre-labelled tissue showed that ACh increased the fractional efflux of ⁴⁵Ca²⁺ whereas L-alanine had no such effect. Both ACh and L-alanine stimulated the release of ⁸⁶Rb⁺ from pre-labelled tissues. The L-alanine-evoked ⁸⁶Rb⁺ efflux was markedly reduced by pre-treatment with 10^-3 M ouabain which had no effect on the ACh-induced response. L-alanine had no significant effect on amylase secretion whereas ACh elicited a marked increase in amylase output. These results show that although both ACh and L-alanine evoke depolarization of the pancreatic acinar cell membrane, the mechanisms underlying their actions on the cells are different.