L-alanine evokes opening of single Ca2+-activated K+ channels in rat liver cells

Cellular uptake of neutral amino acids via Na⁺ cotransporters is known to be associated with an increased membrane K⁺ conductance mediated by an unknown mechanism that is essential for avoiding excessive cell swelling. We now demonstrate by patch-clamp single-channel current recording that exposure of rat liver cells to L-alanine, but not the poorly transported D-stereoisomer, evokes opening of single K⁺ channels and that this effect is reversible upon removal of the amino acid. The nature of the conductance pathways opened in the intact cell by L-alanine has been investigated in cell-free excised membrane patches where it can be shown that the K⁺-selective channels are opened by Ca²⁺ acting from the inside of the membrane at a concentration as low as 0.1 M.