Correlation of NADH and Ca2+ signals in mouse pancreatic acinar cells

Relationships between calcium signals and NADH responses were investigated in pancreatic acinar cells stimulated with calcium-releasing secretagogues. Cytosolic calcium signals were studied using Fura Red or calcium-sensitive Cl- current. Mitochondrial calcium was measured using Rhod-2. The highest levels of NADH autofluorescence were found around the secretory granule region. Stimulation of cells with physiological doses of cholecystokinin (CCK) triggered slow oscillations of NADH autofluorescence. NADH oscillations were clearly resolved in the mitochondrial clusters around secretory granules. Very fast apical calcium signals induced by acetylcholine (ACh) produced no detectable changes in NADH; slightly more extended apical (or preferentially apical) calcium transients triggered clear NADH responses. Triple combined recordings of cytosolic calcium, mitochondrial calcium and NADH revealed the sequence of development of individual signals: an increase in cytosolic calcium was accompanied by a slower mitochondrial calcium response followed by a delayed increase in NADH fluorescence. Recovery of cytosolic calcium was faster than recovery of mitochondrial calcium. NADH recovery occurred at elevated mitochondrial calcium levels. During the transient cytosolic calcium oscillations induced by intermediate doses of ACh, there was an initial increase in NADH fluorescence following the first calcium transient; each of the subsequent calcium responses produced biphasic NADH changes comprising an initial small decline followed by restoration to an elevated calcium level. During the higher-frequency sinusoidal calcium oscillations induced by higher doses of ACh, NADH responses fused into a smooth rise followed by a slow decline. Supramaximal doses of ACh and CCK produced single large NADH transients.