Abstract: | We have used fluo3-loaded mouse pancreatic acinar cells to investigate the relationshipbetween Ca2+ mobilization andintracellular pH (pHi). TheCa2+-mobilizing agonist ACh (500 nM) induced a Ca2+ release in theluminal cell pole followed by spreading of the Ca2+ signal toward the basolateralside with a mean speed of 16.1 ± 0.3 µm/s. In the presence of anacidic pHi, achieved by blockade of theNa+/H+exchanger or by incubation of the cells in aNa+-free buffer, a slowerspreading of ACh-evoked Ca2+ waveswas observed (7.2 ± 0.6 µm/s and 7.5 ± 0.3 µm/s,respectively). The effects of cytosolic acidification on thepropagation rate of ACh-evokedCa2+ waves were largely reversibleand were not dependent on the presence of extracellularCa2+. A reduction in the spreadingspeed of Ca2+ waves could also beobserved by inhibition of the vacuolarH+-ATPase with bafilomycinA1 (11.1 ± 0.6 µm/s), whichdid not lead to cytosolic acidification. In contrast, inhibition of theendoplasmic reticulum Ca2+-ATPaseby 2,5-di-tert-butylhydroquinone ledto faster spreading of the ACh-evokedCa2+ signals (25.6 ± 1.8 µm/s), which was also reduced by cytosolic acidification or treatmentof the cells with bafilomycin A1.Cytosolic alkalinization had no effect on the spreading speed of theCa2+ signals. The data suggestthat the propagation rate of ACh-induced Ca2+ waves is decreased byinhibition of Ca2+ release fromintracellular stores due to cytosolic acidification or toCa2+ pool alkalinizationand/or to a decrease in the proton gradient directed from theinositol 1,4,5-trisphosphate-sensitiveCa2+ pool to the cytosol. |