Sakuma N, Ishikawa S, Okada K, Miyazaki J, Saito T
Department of Medicine, Jichi Medical School, Tochigi, Japan.
Eur J Endocrinol. 1995 Aug;133(2):227-34. doi: 10.1530/eje.0.1330227.
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+]i) 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+]i and insulin secretion disappeared. Also, L-leucine and L-arginine increased [Ca2+]i and induced insulin secretion. Under Ca2+ -free conditions, insulin release was still induced, without any change in [Ca2+]i, 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 of Ca2+. Forskolin, a diterpene activator of adenylate cyclase, produced insulin secretion independently of [Ca2+]i, 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. Spermatogonial proliferation is under the control of FSH, whereas the survival of germ cells is dependent on Sertoli cell function. The observed rise in the number of mitotically inactive Ad-spermatogonia can be explained by a transformation of Ap-spermatogonia into resting Ad-spermatogonia.
本研究旨在确定胰腺β细胞系MIN6中是否存在葡萄糖诱导胰岛素分泌的钙依赖性和非钙依赖性途径。16.7 mmol/l的葡萄糖可导致细胞内游离钙（[Ca2+]i）和胰岛素分泌显著增加，这依赖于葡萄糖代谢。当细胞用20 mmol/l的甘露庚酮糖（一种葡萄糖激酶抑制剂）预处理时，16.7 mmol/l的葡萄糖诱导的[Ca2+]i升高和胰岛素分泌消失。此外，L-亮氨酸和L-精氨酸可增加[Ca2+]i并诱导胰岛素分泌。在无钙条件下，这三种不同的刺激物仍可诱导胰岛素释放，而[Ca2+]i无任何变化。胰岛素分泌的累积值为对照的13.7 - 29.3%，显著低于有钙存在时的值。无论有无钙存在，所有这些刺激物均可引起细胞碱化。佛司可林（一种腺苷酸环化酶的二萜激活剂）可独立于[Ca2+]i产生胰岛素分泌，并伴有细胞碱化。此外，无论有无钙存在，高糖水平均可增加细胞内环磷酸腺苷（cAMP）的产生，且在无钙条件下该效应降低约73%。这些结果表明，高糖水平可刺激胰腺β细胞的钙依赖性和非钙依赖性胰岛素分泌。我们认为，cAMP的产生和细胞碱化参与了非钙依赖性机制。精原细胞增殖受促卵泡激素（FSH）控制，而生殖细胞的存活依赖于支持细胞的功能。观察到的有丝分裂不活跃的Ad-精原细胞数量增加可通过Ap-精原细胞向静止的Ad-精原细胞的转化来解释。
