Influence of calcium on regulatory volume decrease: role of potassium channels.
In most cell types, hyposmotic swelling consistently elicits an increase in the concentration of cytosolic Ca2+ - [Ca2+]i - with contributions of extracellular and intracellular sources. The mechanisms of Ca2+ entry and release from endogenous sources are not fully clarified and may be cell specific. The ubiquity of the swelling-evoked [Ca2+]i rise makes Ca2+ a likely candidate for a role as osmotransducing signal. However, the regulatory volume decrease (RVD) which follows swelling and the osmolyte fluxes involved in this process are not always Ca2+ dependent. It was found that, with a few exceptions, in most cell types the osmosensitive Cl- efflux pathway and the swelling-activated organic osmolyte fluxes are Ca2+ independent. In contrast, Ca2+-dependent or Ca2+-independent K+ fluxes activated by swelling are detected, depending on the cell type. The close correlation found in this review between the Ca2+ dependence of RVD and that of the K+ channels activated by swelling led to the conclusion that it is the type of osmosensitive K+ pathway which largely confers the Ca2+ dependence to RVD. Interestingly, this coincidence of Ca2+-dependent K+ efflux and RVD is found predominantly in epithelial cells, whereas in nonepithelial cells both processes are largely Ca2+ independent. In these cells, the [Ca2+]i rise elicited by swelling may be an epiphenomenon.
Pasantes-Morales
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Department of Biophysics, Institute of Cell Physiology, National University of Mexico, Mexico City, Mexico. hpasante@ifisiol.unam.mx
Morales Mulia
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D000818:Animals; D002118:Calcium / Q000502:physiology*; D020013:Calcium Signaling / Q000502:physiology*; D006801:Humans; D007668:Kidney / Q000166:cytology*; D015221:Potassium Channels / Q000502:physiology*; D014882:Water-Electrolyte Balance / Q000502:physiology*
D015221:Potassium Channels; D002118:Calcium