Adenosine P1 purinoreceptors modulate the cholinoreceptors-mediated intracellular calcium signalling in the acinar cells of submandibular salivary gland

Abstract

The physiological relevance of the adenosine receptors in the functioning of salivary gland acinar cells still remains unclear. Using fluorescent calcium dye fura-2/AM we carried out the measurements of intracellular free calcium concentration ([Ca²⁺]_i) in the acinar cells from submandibular salivary gland during the activation of adenosine receptors. We have found that adenosine itself has no effect on the [Ca²⁺]_i in submandibular cells, although it was able to potentiates acetylcholine- and carbacholine-induced [Ca²⁺]_i transients. Besides, the ability of adenosine to potentiate [Ca²⁺]_i transients was observed only when agonist was used in concentrations less than sub-maximal. We conclude that functioning adenosine receptors are present in the submandibular acinar cells and their activation lead to alteration in the phospholipase C - InsP₃ signaling pathway instead of directly affecting intracellular calcium signaling. Adenosine-induced potentiation of [Ca²⁺]_i transients observed upon activation of choline receptors could be due to phosphorylation of InsP₃-receptors by cAMP-dependent protein kinases.