The effect of hypoosmotic stress on glycine influx in isolated muscle cells of Cancer irroratus

Abstract

AbstractWhen the rock crab Cancer irroratus is exposed to hypoosmotic artificial seawater (ASW) its muscle cell volume is regulated, in part, by a reduction of the intracellular glycine concentration. Therefore, the effect of reduced ASW osmolarity on the unidirectional glycine influx and efflux of isolated rock crab muscle cells was assessed to determine whether changes in these fluxes might contribute to the decreased intracellular glycine concentration. The glycine influx (extracellular glycine concentration = 1mM) into muscle cells exposed to 60% ASW decreased from 810 nmol/g dry wt × 8 min (100% ASW) to 470 nmole/g dry wt × 8 min, whereas the glycine efflux increased from 3,410 nmole/g dry wt × 8 min (100% ASW) to 5,930 nmole/g dry wt × 8 min. The decrease in influx was due to the reduced osmolarity rather than the reduced Na+ concentration of the 60% ASW. Further, even the total replacement of Na+ (Li+ and Tris substituted) reduced the glycine influx by only 34%. Thus Na+‐coupled glycine influx is not an important factor in adjusting the intracellular glycine concentration of muscle cells exposed to reduced ASW osmolarity. Since under isosmotic conditions glycine efflux exceeds influx by a factor of four, the hypoosmotically induced increase in glycine efflux is largely responsible for the decrease of the intracellular glycine concentration during the initial stages of hypoosmotic stress.