In vivo adaptative regulation of muscarinic receptors and muscarinic stimulation-induced Ca2+ mobilization during short-term heat exposure in rat parotid glands

Abstract

1. Adaptation of muscarinic receptors (MR)—muscarinic stimulation—induced intracellular Ca²⁺ mobilization during short-heat exposure (33°C).

2. Heat-exposure for 48 hr decreased the carbachol (CCh)-stimulated cytosolic C²⁺ concentration increase.

3. The number of MR on cell surface increased transiently at 24 hr with a subsequent decrease at 48 hr.

4. CCh-stimulated inositol trisphosphate (IP₃) formation decreased at 48 hr.

5. In saponin-permeabilized cells, 1,4,5-IP₃-induced ⁴⁵Ca²⁺ release decreased at 24 hr.

6. The data suggest that the adaptation for increased muscarinic stimulation occurs at IP₃ generating sites as well as at intracellular IP₃ receptor sites during heat exposure.