CA2- RECHARGING OF APICAL CA2+ STORES BY FOCAL CA2+ ENTRY THROUGH BASAL MEMBRANE PATCH( FLOW VIA TUNNELS IN POLARIZED CELLS )

Intracellular Ca2+ store depletion induces Ca2+ entry across the plasm a membrane, allowing the store to recharge. In our experiments, Ca2+ s tores in pancreatic acinar cells were depleted by acetylcholine (ACh) stimulation in Ca2+-free solution. Thereafter, Ca2+ entry was only all owed through a CaCl2-containing pipette attached to the basal membrane . Recharging intracellular Ca2+ stores via a patch pipette occurred wi thout a rise in the cytosolic Ca2+ concentration and depended on the o peration of a thapsigargin-sensitive Ca2+ pump. After a period of foca l Ca2+ entry, ACh could again evoke a rise in the cytosolic Ca2+ conce ntration, and this rise always started in the apical secretory pole. R echarging the apical Ca2+ store therefore depends on Ca2+ flow through a tunnel from the basal to the secretory pole, and the endoplasmic re ticulum Ca2+ pump is essential for this process.