Ca2+ uptake in GH(3) cells during hypotonic swelling: The sensory role of stretch-activated ion channels

Hypotonic cell swelling triggers an increase in intracellular Ca2+ concentration that is deemed responsible for the subsequent regulated volume decrease in many cells. To understand the mechanisms underlying this increase, we have studied the Ca2+ sources that contribute to hypotonic cell swelling-induced Ca2+ increase (HICI) in GH(3) cells. Fura 2 fluorescence of cell populations revealed that extracellular, but not intracellular, stores of Ca2+ were required. HICI was abolished by nifedipine, a blocker of L-type Ca2+ channels, and Gd3+, a nonspecific blocker of stretch-activated channels (SACs), suggesting two components for the Ca2+ membrane pathway: L-type Ca2+ channels and SACs. Using HICI as an assay, we found that venom from the spider Grammostola spatulata could block. HICI without blocking L-type Ca2+ channels. The venom did, however, block SAC activity. This suggests that Ca2+-permeable SACs, rather than L-type Ca2+ channels, are the sensing elements for HICI. These results support-the model for volume regulation in which SACs, activated by an increase of the membrane tension during hypotonic cell swelling, trigger HICI, leading to a volume decrease.