Developmental regulation of a novel outwardly rectifying mechanosensitive anion channel in Caenorhabditis elegans

The nematode Caenorhabditis elegans offers unique experimental advantages for defining the molecular basis of anion channel function and regulation. However, the relative inaccessibility of somatic cells in adult animals greatly limits direct electrophysiologcal studies of channel activity. We developed methods to routinely isolate and patch clamp C. elegans embryo cells and oocytes and to culture and patch clamp neurons and muscle cells. Dissociated embryonic cells express a robust outwardly rectifying anion current that is activated by membrane stretch and depolarization. This current, termed I-Cl,I-mec, is inhibited by anion and mechanosensitive channel inhibitors. I-Cl,I-mec has broad anion selectivity and the channel has a unitary conductance of 5-7 picosiemens. I-Cl,I-mec is not detectable in whole-cell or isolated patch recordings from oocytes, cultured muscle cells, and cultured neurons but is expressed in single cell and later embryos. Channel density is high, and the current is observed in >80% of membrane patches. Macroscopic currents of 40-120 pA at +100 mV are typically observed in inside-out membrane patches formed using low resistance patch pipettes. Isolated membrane patches of early embryonic cells therefore contain 60-200 I-Cl,I-mec channels. The apparent activation of I-Cl,I-mec shortly after fertilization and its down-regulation in terminally differentiated cells suggests that the channel may play important roles in embryogenesis and/or cytokinesis.