Effects of Potassium Ions on Insulin Release in the Rat from the Perifused Islets of Langerhans with Slow-rise Glucose Stimulation

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The role of extracellular potassium ions in the mechanism of glucose-induced insulin release in the rat was investigated by both dynamic and kinetic analyses of insulin release from islets of Langerhans by slow-rise glucose stimulation in the presence of 6.2 or 12.4 mM K^+, or in its absence. The dose-response curves were sigmoidal in profile with a tendency to show a similar maximal rate of insulin release, but the K_m values were very different. In particular, removal of potassium ions from the medium reduced the K_m value from 8.9 mM (control) to 3.7 mM glucose. Hill's constant (n) was reduced from 5.7 (control) to 4.2 in the absence of K^+ and 4.4 in the presence of 12.4 mM K^+. The Hill plots were linear with slopes of 4.2 (0 mM K^+) and 5.7 (6.2 mM K^+), respectively, whereas in the presence of 12.4 mM K^+ the Hill plot consisted of two straight lines with a break at 4.7 mM glucose (n=1.4 and 4.4). In conclusion, it is suggested that potassium ions in the medium play important roles not only as an electrolyte in connection with the integrity of the B cell membrane, but also as a heterotropic inhibitory effector in the allosteric interaction between the glucoreceptors, leading to a depression of insulin release at low glucose concentrations.
公益社団法人日本薬学会の論文
1979-09-25