Amino acid-evoked membrane potential and resistance changes in pancreatic acinar cells

The effect of some neutrall-amino acids, alanine, valine and proline, on the pancreatic acinar cell membrane potential and resistance was investigated. Simultaneous recordings were made with two intracellular microelectrodes on isolated superfused segments of mouse pancreas. Amino acids were applied by inclusion at known concentrations in the superfusion fluid or by microionophoresis from extracellular micropipettes.l-Alanine (10 mmol·l^–1) evoked a maximal membrane depolarization of about 18 mV. A just detectable depolarization was observed at 0.1 mmol·l^–1 (3 mV). Halfmaximal depolarization was observed at 1.6 mmol·l^–1.d-Alanine had virtually no effect.Microionophoretic applications ofl-alanine,l-valine orl-proline evoked depolarization and resistance reduction with a very short delay (<50 ms). The dose response curves for depolarization and resistance reduction were similar.The amplitude of the depolarization evoked byl-alanine,l-valine andl-proline depended linearly on the level of the pre-set membrane potential (membrane potential could be changed by direct current injection). With decreasing intracellular negativity there was a decrease in the size of the amino acid-evoked depolarization. When the membrane potential was inside positive the amplitude became very small. Extrapolation of the linear relations between membrane potential and size of depolarization revealed a null potential of +20 to +45 mV.Thel-alanine-evoked depolarization was acutely reduced but not abolished by replacing extracellular Na by Tris or Li.l-Alanine,l-proline andl-valine exhibited mutual inhibition of evoked depolarization even when the depolarizing effect of the first applied amino acid was balanced by direct current injection.It is concluded that severall-amino acids act on the pancreatic acinar plasma membrane by opening conductance pathways mainly permeable to Na.