Pancreatic β cells from db/db mice show cell-specific [Ca2+]i and NADH responses to glucose but not to α-ketoisocaproic acid

Objective: We recently showed that timing and magnitude of the glucose-induced cytoplasmic calcium [Ca2+](i) response are reproducible and specific for the individual beta cell. We now wanted to identify which step(s) of stimulus-secretion coupling determine the cell specificity of the [Ca2+](i) response and whether cell specificity is lost in beta-cells from diabetic animals. Besides glucose, we studied the effects of glyceraldehyde, a glycolytic intermediate, and alpha-ketoisocaproic acid (KIC), a mitochondrial substrate. Methods: Early [Ca2+](i) changes were studied stimulations in fura-2 labeled dispersed b cells from lean, ob/ob, and db/db mice. Lag time and peak height were compared during 2 consecutive stimulations with the same stimulator. Nicotinamide adenine dinucleotide ( NADH) responses to glucose and KIC were studied as a measure of metabolic flux. Results: Both glyceraldehyde and KIC induced cell-specific temporal responses in lean mouse b cells with a correlation between lag times for [Ca2+](i) rise during the first and second stimulation. beta Cells from ob/ob and db/db mice showed cell-specific temporal [Ca2+](i) responses to glucose and glyceraldehyde but not to KIC. Glucose induced cell-specific NADH responses in all 3 models, but KIC did so only in lean mouse b cells. Conclusions: A cell-specific response may be induced at several steps of beta-cell stimulus-secretion coupling. Mitochondrial metabolism generates a cell-specific response in normal beta cells but not in db/db and ob/ ob mouse beta cells.