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
✍ Scribed by Akihiro Hazama; Yasunobu Okada
- Publisher
- Springer
- Year
- 1990
- Tongue
- English
- Weight
- 535 KB
- Volume
- 416
- Category
- Article
- ISSN
- 0031-6768
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✦ Synopsis
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 C1-conductances. Biphasic increase in the cytosolic free Ca 2 + concentration ([Ca 2 +]i) were observed by microspectrofluorometry, in fura-2-1oaded cells upon hypotonic stress. Electrophysiological studies with CaZ+-selective and conventional microelectrodes indicated that a biphasic [Ca2 +]t increase was associated with a biphasic hyperpolarization, whereas an interposing [Ca 2 +]~ decrease coincided with a transient depolarization. A Ca 2 + ionophore, ionomycin, produced a sustained Ca 2+ 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 stilbenederivative C1-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+]~ 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 C1-conductance nor a prerequisite for regulatory volume decrease in epithelial cells exposed to a hypotonic solution.