An early transient current is associated with hyposmotic swelling and volume regulation in embryonic chick cardiac myocytes

Hyposmotically induced changes in membrane conductance were measured in embryonic chick cardiac myocytes using conventional and perforated patch-clamp recording techniques; simultaneous measurements of cell volume were made from the video image of the voltage-clamped cell. Hyposmotic challenge was associated with a rapid, transient current coincident with the onset of cell swelling; cell volume subsequently recovered towards control values (regulatory volume decrease; RVD). The transient swelling-induced current (I-swell) reversed at +15 mV, and was not found to be carried exclusively by any single ion in the physiological solutions. I-swell was abolished by gadolinium (Gd3+), a blocker of stretch-activated ion channels, and was absent when the cytoskeleton was disrupted by treatment with cytochalasin B. I-swell was also prevented when intracellular [Ca2+] was buffered with BAPTA AM. Under those experimental conditions which prevented the generation of I-swell, cell volume regulation failed so that the cells remained swollen in hyposmotic solution. Our data reveal a functional relationship between I-swell and RVD, whereby I-swell is a necessary prerequisite, although not exclusively sufficient, for volume recovery following cell swelling. We propose that I-swell is an important early signalling event which activates subsequent mechanisms to regulate cell volume.