Hypotonic swelling or stretch does not change cytosolic calcium in mouse renal juxtaglomerular cells

This study aimed to examine the influence of cell swelling and of direct mechanical stretch on the cytosolic calcium concentration in mouse renal juxtaglomerular cells. To this end JG cells located in isolated mouse renal afferent arterioles were exposed to hypotonic extracellular fluid to cause cell swelling or were mechanically stretched and cytosolic calcium was monitored with fura-2 calcium microspectrofluorimetry. None of the above mentioned manoeuvres caused an increase of cytosolic calcium in the juxtaglomerular cells, which all responded to ionomycin (5 micrograms mL-1) with a marked calcium mobilization. Exposure of cultured rat renal mesangial cells to hypotonic buffer or direct mechanical stress increased cytosolic calcium in 90% of the cells under investigation. These findings suggest that cell swelling or an increased stretch of the plasma membrane of juxtaglomerular cells located in renal afferent arterioles does not lead to measurable increases of the cytosolic calcium concentration. It appears less likely therefore that a membrane-stretch regulated calcium influx has a major functional role in JG cells.