POLARIZED CA2-PERMEABILIZED PAROTID ACINAR-CELLS EVOKED BY FLASH-PHOTOLYSIS OF CAGED INOSITOL 1,4,5-TRISPHOSPHATE( RELEASE IN SAPONIN)

In exocrine acinar cells, agonist stimulation results in a polarized C a2+ signal, termed the 'Ca2+ wave', that propagates from the apical po le towards the basolateral region. We attempted to detect the inositol 1,4,5-trisphosphate (InsP(3))-induced Ca2+ wave in saponin-permeabili zed rat parotid acinar cells using a digital imaging system. The perme abilized acinar cells were labelled with the membrane-bound Ca2+ indic ator Calcium Green C-18 to detect changes in Ca2+ concentration adjace nt to the membrane of intracellular organelles. Application of InsP(3) was made by the photolysis of InsP(3) P-4(5)-1-(2-nitrophenyl)ethyl e ster (caged InsP(3)) to expose simultaneously all regions of the perme abilized acinar cells to InsP(3). The increase in fluorescence ratio f ollowing the photolysis of 0.5 mu M caged InsP(3) started at the apica l region of the acinar cells within 0.1 s and spread towards the basol ateral region, indicating that Ca2+ release from intracellular Ca2+ st ores was initially evoked at the apical region. Pretreatment with thap sigargin, an inhibitor of endoplasmic reticulum Ca2+ pumps, failed to prevent the InsP(3)-induced Ca2+ wave, suggesting that the generation of the Ca2+ wave is not attributed to the polarized distribution of th e Ca2+ pumps. The photolysis of a high concentration (10 mu M) of cage d InsP(3) caused a homogeneous increase in the fluorescence ratio thro ughout the cells, indicating that all regions of intracellular Ca2+ st ores similarly responded to the high concentration of InsP(3). The pre sent study is the first demonstration of the InsP(3)-induced Ca2+ wave in permeabilized exocrine acinar cells. The result provides fresh evi dence that the apical region contains elements of intracellular Ca2+ s tores particularly sensitive to InsP(3) and that the Ca2+ wave results from a polarized distribution of InsP(3)-sensitive Ca2+ stores.