Functional contribution of stretch-activated channels in osmotic reactions and calcium signaling in mammalian cells

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10th International Congress & quot-Cell Volume Regulation: Novel Therapeutic Targets and Pharmacological Approaches& quot-
Chubinskiy-Nadezhdin, V.I., Sudarikova, A.V., Negulyaev, Yu.A., and Morachevskaya, E.A.
Laboratory ofIonic Mechanisms of Cell Signaling, Institute of Cytology, Russian Academy of Sciences, St. Petersburg, Russian Federation
Mechanically gated ion channels are involved in processes of volume regulation and calcium signaling in living cells. However, functional contribution of stretch-activated cation channels (SACs) into volume-dependent Ca2+ signaling remains unclear [1, 2]. Calcium-permeable gadolinium-blocking SACs have been previously characterized in human myeloid leukemia K562 cells [3, 4]. Here, changes in intracellular free ionized Ca2+ concentration ([Ca2+i]) in K562 cells were monitored in response to reduced bath osmolarity using Fura-2 imaging. Cell swelling induced by decrease of extracellular osmolality resulted in the elevation of [Ca2+J. Ca2+ entry could be blocked by external application of Gd3+ ions thus confirming that SACs in plasma membrane mediate swelling-induced Ca2+ influx in leukemia K562 cells. In single channel studies, functional impact of membrane cholesterol and actin cyto-skeleton on mechanosensitive channel activity in leukemia cells has been analysed [5, 6]. We found that cholesterol depletion-induced suppression of stretch-activated channels was mediated via actin rearrangement. In cell-attached patch clamp experiments on breast cancer MCF7 cells and transformed fibroblasts 3T3B-SV40 we observed typical SAC activity followed by transient activation of K+ channels (8−10 pS). Importantly, K+ currents displayed no
direct mechanosensitivity. Our results indicate that Ca2±dependent K+ channels could be activated by Ca2+ influx via colocalized SACs in membrane patch. The observed effect represents the functional coupling between SACs and K+ channels in plasma membrane. In sum, the data imply that SAC activation underlies putative global and local calcium signa-
ling mechanisms involved in volume regulation in mammalian cells.
The work was supported by RFBR and OPTEC grant for young investigators (2013).
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Бюллетень сибирской медицины, 2013, том 12, № 4, с. 24−68

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