Transformation of local Ca2+ spikes to global Ca2+ transients: the combinatorial roles of multiple Ca2+ releasing messengers

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Abstract
In pancreatic acinar cells, low, threshold concentrations of acetylcholine (ACh) or cholecystokinin (CCK) induce repetitive local cytosolic Ca2+ spikes in the apical pole, while higher concentrations elicit global signals. We have investigated the process that transforms local Ca2+ spikes to global Ca2+ transients, focusing on the interactions of multiple intracellular messengers. ACh‐elicited local Ca2+ spikes were transformed into a global sustained Ca2+ response by cyclic ADP‐ribose (cADPR) or nicotinic acid adenine dinucleotide phosphate (NAADP), whereas inositol 1,4,5‐trisphosphate (IP3) had a much weaker effect. In contrast, the response elicited by a low CCK concentration was strongly potentiated by IP3, whereas cADPR and NAADP had little effect. Experiments with messenger mixtures revealed a local interaction between IP3 and NAADP and a stronger global potentiating interaction between cADPR and NAADP. NAADP strongly amplified the local Ca2+ release evoked by a cADPR/IP3 mixture eliciting a vigorous global Ca2+ response. Different combinations of Ca2+ releasing messengers can shape the spatio‐temporal patterns of cytosolic Ca2+ signals. NAADP and cADPR are emerging as key messengers in the globalization of Ca2+ signals.