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 microM.