Inhibition by thiocyanate of muscarinic-induced cytosolic acidification and Ca2+ entry in rat sublingual acini

Thiocyanate (SCN−) plays a critical part in an oral antimicrobial system by acting as a substrate for peroxidases. Salivary glands concentrate SCN− from blood up to 5 mM in saliva; however, the influence of SCN− on salivary acinar-cell function is unknown. The present study examined the effects of SCN− on the regulation of cytosolic pH (pHi) and free Ca2+ concentration ([Ca2+]i) in rat sublingual mucous acini using the pH- and Ca2+-sensitive fluorescent indicators, 2′,7′-bis-(2-carboxyethyl)-5,6-carboxyfluorescein and fura-2, respectively. SCN− induced a concentration-dependent inhibition of the carbachol-stimulated cytosolic acidification (K12, approx. 1.4mM SCN−). Cytosolic pH recovery from an acid load was not changed by substitution of Cl− by SCN−, suggesting that Na+/H+ exchange activity was not affected by SCN−. SCN− did not alter the initial carbachol-stimulated increase in [Ca2+]i; however, the sustained [Ca2+]i increase was inhibited by >65% (K12, approx. 1.0 mM SCN−). Furthermore, SCN− prevented the carbachol-stimulated Mn2+ influx, indicating that it inhibits the divalent-cation entry pathway. Consistent with decreased Ca2+ mobilization being involved in the blockade of the agonist-induced acidification by SCN−, only total replacement of Cl− with SCN− significantly inhibited the acidification induced by the Ca2+ ionophore ionomycin. The permeability to SCN− through the Ca2+-dependent Cl− channels was 5.2-fold higher than the permeability to Cl−. These results suggest that inhibition of the agonist-induced cytosolic acidification by high-concentration SCN− may be mediated by both competitive inhibition of HCO3− efflux and by blockade of Ca2+ influx.