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Glucose induces calcium-dependent and calcium-independent insulin secretion from the pancreatic beta cell line MIN6

Sakuma N, Ishikawa S, Okada K, Miyazaki J, Saito T, Glucose induces calcium-dependent and calcium-independent insulin secretion from the pancreatic beta cell line MIN6. Eur J Endocrinol 1995;133:227–34. ISSN 0804–4643

The present study was undertaken to determine whether there are Ca²⁺-dependent and -independent pathways of glucose-induced insulin secretion from the pancreatic beta cell line MIN6. Glucose at a concentration of 16.7 mmol/l caused marked increases in cellular free calcium [Ca²⁺]₁) and insulin secretion, which depended on glucose metabolism. When cells were pretreated with 20 mmol/l mannoheptulose, an inhibitor of glucokinase, the 16.7 mmol/l glucose induced a rise in [Ca²⁺]₁ and insulin secretion disappeared. Also, L-leucine and L-arginine increased [Ca²⁺]₁ and induced insulin secretion. Under Ca²⁺-free conditions, insulin release was still induced, without any change in [Ca²⁺]₁, by these three different stimulants. The cumulative values of insulin secretion were 13.7–29.3% of the control, which were significantly less than that in the presence of Ca²⁺. Cellular alkalinization occurred in response to all these stimulants, irrespective of the presence or absence of Ca²⁺. Forskolin, a diterpene activator of adenylate cyclase, produced insulin secretion independently of [Ca²⁺]₁, which accompanied cellular alkalinization. Also, a high glucose level increased cellular cyclic AMP (cAMP) production in the presence and absence of Ca²⁺, and the effect was diminished by approximately 73% in Ca²⁺-free conditions. These results indicate that a high glucose level stimulates both Ca²⁺-dependent and -independent insulin secretion from pancreatic beta cells. We suggest that the cAMP production and the cellular alkalinization participate in the Ca²⁺-independent mechanism.

Nobuko Sakuma, Division of Endocrinology and Metabolism, Department of Medicine, Jichi Medical School, 3311-1 Yakushiji Minamikawachi-machi, Tochigi 329-04, Japan

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				N. Itabashi, K. Okada, S. Muto, N. Fujita, T. Ohta, J.-i. Miyazaki, Y. Asano, and T. Saito A Novel Enhancer of Insulinotrophic Action by High Glucose (JTT-608) Stimulates Insulin Secretion from Pancreatic beta -Cells via a New Cellular Mechanism J. Pharmacol. Exp. Ther., June 1, 2001; 297(3): 953 - 960. [Abstract] [Full Text]