EFFECT OF INTRACELLULAR PH ON ACETYLCHOLINE-INDUCED CA2-CELLS( WAVES IN MOUSE PANCREATIC ACINAR)

We have used flue 3-loaded mouse pancreatic acinar cells to investigat e the relationship between Ca2+ mobilization and intracellular pH (pH( i)). The Ca2+-mobilizing agonist ACh (500 nM) induced a Ca2+ release i n the luminal cell pole followed by spreading of the Ca2+ signal towar d the basolateral side with a mean speed of 16.1 +/- 0.3 mu m/s. In th e presence of an acidic pHi, achieved by blockade of the Na+/H+ exchan ger or by incubation of the cells in a Na+-free buffer, a slower sprea ding of ACh-evoked Ca2+ waves was observed (7.2 +/- 0.6 mu m/s and 7.5 +/- 0.3 mu m/s, respectively). The effects of cytosolic acidification on the propagation rate of ACh-evoked Ca2+ waves were largely reversi ble and were not dependent on the presence of extracellular Ca2+. A re duction in the spreading speed of Ca2+ waves could also be observed by inhibition of the vacuolar Hi-ATPase with bafilomycin Al (11.1 +/- 0. 6 mu m/s), which did not lead to cytosolic acidification. In contrast, inhibition of the endoplasmic reticulum Ca2+-ATPase by 2,5-di-tert-bu tylhydroquinone led to faster spreading of the ACh-evoked Ca2+ signals (25.6 +/- 1.8 mu m/s), which was also reduced by cytosolic acidificat ion or treatment of the cells with bafilomycin Al. Cytosolic alkaliniz ation had no effect on the spreading speed of the Ca2+ signals. The da ta suggest that the propagation rate of ACh-induced Ca2+ waves is decr eased by inhibition of Ca2+ release from intracellular stores due to c ytosolic acidification or to Ca2+ pool alkalinization and/or to a decr ease in the proton gradient directed from the inositol 1,4,5-trisphosp hate-sensitive Ca2+ pool to the cytosol.