Ionophore A23187-induced Insulin Secretion in the Isolated, Perfused Dog Pancreas

Abstract

Perfusion of ionophore A23187 (10 muM) in the isolated dog pancreas resulted in a monophasic release of insulin. Ionophore A23187 (10 muM) failed, however, to elicit insulin secretion when added to calcium deficient (0.1 mmoles/L) perfusate. Simultaneous reintroduction of calcium (1.27 mmoles/L) and discontinuance of ionophore A23187 following calcium deficient periods caused a monophasic secretion of insulin which was quantitatively very similar (41,400 +/- 13,800 muU) to that stimulated by ionophore during normocalcemic perfusion. With reference to the current literature, these results suggest that ionophore A23187 elicits insulin secretion in the perfused dog pancreas preparation by increasing the level of free intracellular calcium, a process which is dependent upon a normal extracellular ionic calcium concentration.

Identification and metabolism of polyphosphoinositides in isolated islets of Langerhans

“…Consistent with the Ca2+ requirement for breakdown of polyphosphoinositides is the finding that extracellular Ca2+ and Ca2+-mobilized from intracellular pools are required for secretion (Wollheim & Sharp, 1981). Loss of [32p]PO4 from islet polyphosphoinositides was also observed during incubation of islets with ionophores that evoke insulin release and increase the level of free intracellular Ca2+ in islets (Conaway et al, 1976;Malaisse, 1980). Moreover, the secretagogue tolbutamide translocates Ca2+ (Couturier & Malaisse, 1980) and activates Ca2+-dependent phospholipid fatty acid turnover in islets (Laychock, 1983), in addition to its effect on polyphosphoinositide breakdown.…”

Insulin secretion: The nitric oxide controversy

“…On balance, cNOS-derived NO seems to stimulate insulin release while iNOS-derived NO inhibits insulin secretion (Nystrom et al, 2012[ 95 ]; Sansbury and Hill, 2014[ 109 ]). The conversion of L-arginine to NO and increased insulin secretion in cell-free preparations of HIT-T15 cells appear to be due to the activity of cNOS, as the Ca 2+ ionophore A23187, which induces insulin secretion (Conaway et al, 1976[ 19 ]), also induces NO release from HIT-T15 cells (Schmidt et al, 1992[ 110 ]). In addition, insulin secretion is correlated with the intracellular concentration of NADPH (Attie, 2015[ 7 ]), Ca 2+ (Conaway et al, 1976[ 19 ]), and calmodulin (Dadi et al, 2014[ 23 ]) which all are necessary for cNOS activation.…”

“…The conversion of L-arginine to NO and increased insulin secretion in cell-free preparations of HIT-T15 cells appear to be due to the activity of cNOS, as the Ca 2+ ionophore A23187, which induces insulin secretion (Conaway et al, 1976[ 19 ]), also induces NO release from HIT-T15 cells (Schmidt et al, 1992[ 110 ]). In addition, insulin secretion is correlated with the intracellular concentration of NADPH (Attie, 2015[ 7 ]), Ca 2+ (Conaway et al, 1976[ 19 ]), and calmodulin (Dadi et al, 2014[ 23 ]) which all are necessary for cNOS activation. Low concentrations of NO elevate ATP production and cause K ATP channel closure, while high concentrations of NO are associated with a decrease in ATP production, independent of cGMP (Sunouchi et al, 2008[ 123 ]).…”

Effect of Somatostatin on Insulin Secretion Induced by lonophore A23187

“…Cyclic somatostatin (Bachem, Inc.) and ionophore A23187 (generously supplied by Dr. Robert Hamill, Eli Lilly and Co.) were added as required. A23 187 was dissolved in ethanol before being added to the desired perfusate (11). Insulin was determined by a modification (11) of the coated charcoal immunoassay procedure described by Herbert et al (12).…”