Towards understanding physiological function of TRPM6/7 like channel in a HCO_3-secreting epithelium

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Ruminant parotid glands secrete continuously large volumes of HCO_3-rich saliva even at resting, but the underlying molecular mechanism remains unclear. Since ruminant parotid secretory cells contain several ion channels that can be regulated by intracellular Ca^<2+> and Mg^<2+>, resting cellular homeostasis of these divalent cations might also play an important role in the continuous HCO_3 secretion. Towards better understanding the mechanism of the parotid HCO_3 secretion, this project focused on TRPM6 and TRPM7 that are known to be cation channels permeable to divalent cations such as Ca^<2+> and Mg^<2+>. Using electrophysiological and molecular biological techniques, it was found that 1) bovine parotid acinar cells exhibit a membrane current, which is sensitive to intracellular Mg^<2+> as reported for recombinant TRPM7 and TRPM6 currents, 2) bovine parotid cells express transcripts of TRPM6 and TRPM7, 3) TRPM7 that was cloned from bovine parotid was functional in a heterologous expression system. These basic results would be useful for future studies to address the issues as to not only the molecular basis and cellular regulation of the native TRPM6/7-like conductance in bovine parotid acinar cells, but also the role of TRPM6 and TRPM7 in epithelial HCO_3 secretion.