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Glucose-stimulated elevation of cytoplasmic calcium is defective in the diabetic Chinese hamster islet B cell

Lindström P. Sehlin J, Frankel BJ. Glucose-stimulated elevation of cytoplasmic calcium is defective in the diabetic Chinese hamster islet B cell. Eur J Endocrinol 1996:134:617–25. ISSN 0804–4643

To characterize insulin release and cytoplasmic free Ca²⁺ [Ca²⁺]_i) levels in the diabetic Chinese hamster islet B cell, islets from genetically normal subline M) and diabetic (subline L) hamsters were collagenase isolated. Insulin release and glucose utilization (conversion of D-[5-³H]glucose to ³H₂O) were measured in whole islets; [Ca²⁺]_i levels were measured in single islet cells using fura-2, The Ca²⁺ channel agonist, 12 mmol/l perchlorate, ClO₄^–, increased the subnormal insulin response during 20 mmol/l glucose perifusion, but did not normalize it. Glucose utilization measured over a 2-h period was normal. Glucose induced an initial decrease and then a rise in [Ca²⁺]_i in 85% of the normal (presumably B) cells. In diabetic cells, the [Ca²⁺]_i response was delayed, subnormal and only observed in 23% of the cells. When perchlorate or another Ca²⁺ channel agonist, 10 µmol/l CGP 28392, was added with glucose, a larger proportion of the diabetic cells (61–67%) showed increased [Ca²⁺]_i and the mean [Ca²⁺]_i response was not different from normal. However, neither perchlorate nor CGP 28392 could normalize glucose-stimulated insulin release, and K⁺-induced insulin release was decreased in diabetic islets. The K⁺ -induced [Ca²⁺]_i rise was essentially normal in all the diabetic islet cells. Therefore, the diabetic hamster islet appears to metabolize glucose normally, but has a diminished insulin response to glucose and K⁺. The Ca²⁺ channel agonists markedly improve the subnormal [Ca²⁺]_i response but not the insulin response. Glucose-induced elevation of [Ca^2–]_i and exocytosis appear defective in the diabetic Chinese hamster B cell.

Per Lindström, Department of Histology and Cell Biology, Umea University, S-901 87 Umea, Sweden