Inhibitors of the intracellular Ca2+ release mechanism prevent muscarinic-induced Ca2+ influx in rat sublingual mucous acini.

The effects of inhibitors of the intracellular Ca2+ release mechanism on divalent cation fluxes were examined in acinar cells loaded with the Ca(2+)-sensitive, Mn(2+)-quenchable dye, fura-2. TMB-8 and dantrolene (DTL) dramatically inhibited the carbachol (CCh)-stimulated increase in [Ca2+]i and Mn2+ influx. These agents do not directly inhibit divalent cation entry since addition of TMB-8 or DTL after CCh stimulation did not block Mn2+ influx. TMB-8 did not influence the [Ca2+]i increase or the Mn2+ influx produced by thapsigargin. These results indicate that TMB-8 and DTL do not interfere with divalent cation influx by inhibiting a step distal to depletion of the intracellular Ca2+ pool. TMB-8 and DTL did not significantly influence the muscarinic-stimulated production of inositol trisphosphate (IP3) and inositol tetrakisphosphate (IP4), although TMB-8, but not DTL, did decrease the CCh-stimulated 1,4,5-IP3 levels approximately 55%. The above results directly demonstrate that the filling state of the intracellular Ca2+ store primarily regulates the Ca2+ entry mechanism in sublingual mucous acinar cells.