Abstract
The difference of Ca 2+ mobilization induced by muscarinic receptor activation between parotid acinar and duct cells was examined. Oxotremorine, a muscarinic–cholinergic agonist, induced intracellular Ca 2+ release and extracellular Ca 2+ entry through store-operated Ca 2+ entry (SOC) and non-SOC channels in acinar cells, but it activated only Ca 2+ entry from non-SOC channels in duct cells. RT-PCR experiments showed that both types of cells expressed the same muscarinic receptor, M3. Given that ATP activated the intracellular Ca 2+ stores, the machinery for intracellular Ca 2+ release was intact in the duct cells. By immunocytochemical experiments, IP 3R2 colocalized with M3 receptors in the plasma membrane area of acinar cells; in duct cells, IP 3R2 resided in the region on the opposite side of the M3 receptors. On the other hand, purinergic P2Y2 receptors were found in the apical area of duct cells where they colocalized with IP 3R2. These results suggest that the expression of the IP 3Rs near G-protein-coupled receptors is necessary for the activation of intracellular Ca 2+ stores. Therefore, the microenvironment probably affects intracellular Ca 2+ release and Ca 2+ entry.
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