Effects of L-arginine on islet NAD(P)H, [Ca2+]i, and hormone secretion.
Gray and black columns and traces represent α- and β-cells, respectively. A, arginine-dependent NAD(P)H responses from intact islets. Islets were perifused at 1 mM glucose (G1) and exposed to step-increases in arginine concentration. Data are normalized to minimal and maximal β-cell NAD(P)H obtained with FCCP and cyanide, respectively. The α-cell NAD(P)H changes to arginine (Arg) were statistically significant (p<0.01, 32 α-cells measured from 10 islets, 3 mice) and α-cell NAD(P)H intensity was different from β-cell intensity for each condition tested (p<0.01). Error bars indicate the standard error of the mean. B, averaged intracellular calcium responses to arginine. Data are expressed in percent change in Fluo-4 intensity compared to baseline at 1 mM glucose. α-cell responses to arginine were significant at all concentrations (p<0.01, n = 42) and β-cell responses were significant at 10 and 20 mM arginine (p<0.01, n = 11). C, intracellular calcium responses to 10 mM arginine from an islet perifused at 1 mM glucose (G1). 2 α-cells from the same islet are presented. Fluo-4 intensity is expressed in arbitrary units. The figure is representative of 11 α-cells from 4 islets. D, glucagon and insulin responses were measured for 9 minutes at 1 mM glucose, and then arginine was perifused at 10 mM for 18 minutes. Finally, glucose was added to the perifusion medium at 12 mM for 18 minutes. Experiment was repeated 4 times, 600 islets from 8 mice were used. Error bars represent the standard error of the mean.
