Patch clamp study of the UNC-105 degenerin and its interaction with the LET-2 collagen in Caenorhabditis elegans muscle

Degenerins have emerged from genetic studies in Caenorhabditis elegans as candidate mechanically gated amiloride-sensitive ion channels for transducing mechanical stimuli into cellular responses. In C. elegans muscle, the existence of a genetic interaction between the unc-105 degenerin gene and let-2, a gene encoding an α2(IV) collagen, raised the possibility that UNC-105 may function as a mechanically gated channel in a stretch receptor complex. However, to date, ion channel activity of UNC-105 has only been recorded in a gain-of-function mutant form in heterologous expression systems. In this study we investigated the in situ properties of UNC-105 using the whole cell configuration of the patch clamp technique on body wall muscle cells from acutely dissected C. elegans. Amiloride was found to be without effect on membrane potential of wild-type muscle cells, suggesting that the UNC-105 degenerin is electrically silent in resting muscle. Hypo-osmotic shocks induced a reversible depolarization of muscle cells but which was not affected by amiloride. Deformation of the cells by applying tension to the filamentous complex on which muscle cells remained attached or by ejecting external solution under pressure failed to induce any change of membrane potential. In gain-of-function unc-105(n506) mutant cells, an amiloride-sensitive inward Na+ current was found to be constitutively active, leading to maintained muscle depolarization. An associated mutation in the α2(IV) collagen LET-2 led to the closure of the mutant UNC-105(n506) channel while a collagenase treatment of these double mutant cells caused it to re-open, giving evidence for a functional interaction between LET-2 collagen and mutant UNC-105 channel.