L-Alanine and L-phenylalanine activate Na+ and K+ conductance pathways in the exocrine mouse pancreas

The effects of some amino acids, L-alanine, L-phenylalanine, DL-alanine, D-alanine and beta-alanine on membrane potential, membrane current, amylase secretion and 45Ca and 86Rb fractional efflux in isolated mouse pancreatic segments were investigated. A two microelectrode voltage clamp technique was applied to study the effects of the amino acids on membrane current. The amino acids evoked dose-dependent (0.05-0.5 mmole) and reversible membrane depolarization and increases in membrane current. The relative potencies of the actions of the amino acids were: L-alanine greater than DL-alanine greater than L-phenylalanine greater than D-alanine greater than beta-alanine. A more detailed study of the action of L-alanine showed that the relationship between the L-alanine-evoked membrane current and membrane potential was virtually linear with reversal of current polarity being observed at a membrane potential of about +30 mV. While the L-alanine-induced increase in membrane conductance was dose-dependent, the reversal potential (EL-ala) was independent of the L-alanine concentration used. Replacement of the normal Na-rich superfusion fluid by a low Na solution (5 mM) markedly reduced the L-alanine-elicited inward current at the normal resting potential. The L-alanine-evoked conductance increase was also reduced in low Na solution and the EL-ala was close to O mV. During the exposure of pancreatic segments to C1 free solution (sulphate substitution) EL-ala was about 12 mV more positive (+ 43.7 +/- 0.8 mV) than during exposure to control solution (+ 31.5 +/- 1.0 mV).(ABSTRACT TRUNCATED AT 250 WORDS)