The effect of inositol 1,3,4,5-tetrakisphosphate on inositol trisphosphate-induced Ga2+ mobilization in freshly isolated and cultured mouse lacrimal acinar cells

Earlier reports have shown a remarkable synergism between InsP(4) and InsP( 3) [either Ins(1,4,5)P-3 or Ins(2,4,5)P-3] in activating Ca2+-dependent Kand Cl- currents in mouse lacrimal cells [Changya, Gallacher, Irvine, Potte r and Petersen (1989) J. Membr. Biol. 109, 85-93; Smith (1992) Biochem. J. 283, 27-30]. However, Bird, Bossier, Hughes, Shears, Armstrong and Putney [ (1991) Nature (London) 352, 162-165] reported that they could see no such s ynergism in the same cell type. A major experimental difference between the two laboratories lies in whether or not the cells were maintained in prima ry culture before use. Here we have compared directly the responses to inos itol polyphosphates in freshly isolated cells versus cells cultured for 6-7 2 h. In the cultured cells, Ins(2,4,5)P-3, at 100 mu M produced a robust st imulation of K+ and Cl- currents, as much as an order of magnitude greater than that observed in the freshly isolated cells. However, the freshly isol ated cells could be restored to a sensitivity similar to cultured cells by the addition of InsP(4), at a concentration two orders of magnitude lower t han that of Ins(2,4,5)P-3,. We discuss the implications of this with respec t to the actions of InsP(4), including the possibility that disruption of t he cellular structure during the isolation of the cells exposes an extreme manifestation of a possible physiological role for InsP(4), in controlling calcium-store integrity.