Temperature-dependent calcium-induced calcium release via InsP3 receptors in mouse olfactory ensheathing glial cells

Cooling can induce Ca²⁺ signaling via activation of temperature-sensitive ion channels such as TRPM8, TRPA1 and ryanodine receptor channels. Here we have studied the mechanism of cooling-evoked Ca²⁺ signaling in mouse olfactory ensheathing cells (OECs), a specialized type of glial cells in the olfactory nerve layer of the olfactory bulb. Reducing the temperature from above 30°C to 28°C and below triggered Ca²⁺ transients that persisted in the absence of external Ca²⁺, but were suppressed after Ca²⁺ store depletion by cyclopiazonic acid. Cooling-evoked Ca²⁺ transients were present in mice deficient of TRPM8 and TRPA1, and were not inhibited by ryanodine receptor antagonists. Inhibition of InsP₃ receptors with 2-APB and caffeine entirely blocked cooling-evoked Ca²⁺ transients. Moderate Ca²⁺ increases, as evoked by flash photolysis of NP-EGTA (caged Ca²⁺) and cyclopiazonic acid, triggered InsP₃ receptor-mediated Ca²⁺ release at 22°C, but not at 31°C. The results suggest that InsP₃ receptors mediate Ca²⁺-induced Ca²⁺ release in OECs, and that this Ca²⁺ release is temperature-sensitive and can be suppressed at temperatures above 28°C.