Biphasic rises in cytosolic free Ca2+ in association with activation of K+ and Cl- conductance during the regulatory volume decrease in cultured human epithelial cells.
During exposure to a hypotonic solution (55% osmolarity), cultured human epithelial (Intestine 407) cells exhibit a regulatory volume decrease after osmotic swelling. This process is known to involve parallel activation of volume-regulatory K+ and Cl- conductances. Biphasic increase in the cytosolic free Ca2+ concentration ([Ca2+]i) were observed by microspectrofluorometry, in fura-2-loaded cells upon hypotonic stress. Electrophysiological studies with Ca2(+)-selective and conventional microelectrodes indicated that a biphasic [Ca2+]i increase was associated with a biphasic hyperpolarization, whereas an interposing [Ca2+]i decrease coincided with a transient depolarization. A Ca2+ ionophore, ionomycin, produced a sustained Ca2+ increase and a prolonged hyperpolarization which was sensitive to the K+ channel blocker, quinine. A subsequent hypotonic challenge gave rise to a depolarization, which was sensitive to a stilbene-derivative Cl- channel blocker, without inducing further changes in [Ca2+]i. Normal cell volume regulation in a hypo-osmotic medium could take place even in the presence of ionomycin. It is concluded that a biphasic [Ca2+]i increase is closely associated with activation of the volume-regulatory K+ conductance, and that the interposing [Ca2+]i decrease is neither a causative factor for activation of the volume-regulatory Cl- conductance nor a prerequisite for regulatory volume decrease in epithelial cells exposed to a hypotonic solution.
Hazama
A
A
Department of Physiology, Kyoto University, Faculty of Medicine, Japan.
Okada
Y
Y
D001692:Biological Transport / Q000187:drug effects / Q000502:physiology; D002118:Calcium / Q000378:metabolism* / Q000502:physiology; D002460:Cell Line; D002712:Chlorides / Q000493:pharmacokinetics*; D003600:Cytosol / Q000378:metabolism*; D004553:Electric Conductivity / Q000187:drug effects / Q000502:physiology; D004594:Electrophysiology; D004847:Epithelial Cells; D004848:Epithelium / Q000378:metabolism / Q000502:physiology; D016257:Fura-2; D006801:Humans; D007413:Intestinal Mucosa / Q000378:metabolism; D007422:Intestines / Q000166:cytology* / Q000502:physiology; D015759:Ionomycin / Q000494:pharmacology; D008839:Microelectrodes; D011188:Potassium / Q000493:pharmacokinetics*; D011803:Quinine / Q000494:pharmacology
D002712:Chlorides; D015759:Ionomycin; D011803:Quinine; D011188:Potassium; D002118:Calcium; D016257:Fura-2