Lactate modulates the intracellular pH sensitivity of human TREK1 channels

Tissue acidosis and high lactate concentrations are associated with cerebral ischaemia. The degree of acidosis is dependent on circulating glucose concentration, hyperglycaemia being associated with increased acidosis. Among other agents, lactate and protons have been shown to activate the leak potassium channel; TREK1 (TWIK related potassium channel 1) from the intracellular side and its increased activity is implicated in tolerance towards ischaemic cell damage. In the present study, we show that ischaemic concentrations of lactate (30 mM) at pH 7.0 and 6.5, commonly observed during ischemia, cause robust potentiation of human TREK1 (hTREK1) activity at single-channel level in cell-free inside-out membrane patches, while 30 mM lactate at pH 6.0 to 5.5, commonly observed during hyperglycaemic ischemia, reduces hTREK1 channel activity significantly. The biphasic effect of 30 mM lactate (ischaemic concentrations) on modulation of hTREK1 by varying pH conditions is specific since basal concentrations of lactate (3 mM) and 30 mM pyruvate at pH 7.0 and 5.5 failed to show similar effect as lactate. Experiments with deletion and point mutants of hTREK1 channel suggest that lactate changes the pH modulation of hTREK1 by interacting differently with the histidine residue at 328th position (H328) above and below its pKa (∼6.0) in the intracellular carboxyl-terminal domain of TREK1. This lactate-induced pH modulation of hTREK1 is absent in C-terminal deletion mutant, CTDΔ100, and is similar in E321A-hTREK1 mutant as in wild-type hTREK1 suggesting that it is independent of pH-sensitive glutamate residue at 321st position. Such a differential pH-dependent effect of lactate on an ion channel function has not been reported earlier and has important implications in different stages of ischaemia.