Somatostatin inhibits insulin secretion by a G-protein-mediated decrease in Ca2+ entry through voltage-dependent Ca2+ channels in the beta cell.
Somatostatin inhibits insulin secretion by a G-protein-mediated decrease in Ca2+ entry through voltage-dependent Ca2+ channels in the beta cell.
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发表时间：
1991-01
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通讯作者：
W. Hsu;H. Xiang;A. Rajan;D. Kunze;A. E. Boyd
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作者：
W. Hsu;H. Xiang;A. Rajan;D. Kunze;A. E. Boyd
我们验证了生长抑素(SRIF)通过影响电压依赖性钙通道而抑制SV40转化的仓鼠β细胞系(HIT细胞)胰岛素分泌的假设，并考察了G蛋白是否参与了这一过程。用全细胞膜片钳方法记录细胞内游离钙电流，用Fura-2测定细胞内游离钙离子浓度，用放射免疫法测定细胞内cAMP和胰岛素的分泌。SRIF在10(-12)-10(-7)M范围内以剂量依赖的方式抑制钙电流、[Ca~(2+)]i和基础胰岛素分泌。K+(15 MM)去极化或钙通道激动剂引起的[Ca~(2+)]i和胰岛素分泌增加。SRIF在10(-12)~10(-7)M范围内呈剂量依赖性地抑制Bay K 8644细胞的胰岛素分泌，其半数抑制浓度(IC50)分别为8.6×10(-12)M和8.3×10(-11)M，抑制K+和Bay K 8644诱导的[Ca~(2+)]i升高的IC50分别为1×10(-10)M和2.9×10(-10)M。SRIF还可减弱cAMP升高剂异丁基甲基黄嘌呤(1 MM)在葡萄糖存在下引起的[Ca~(2+)]i升高。BAY K8644、K+和SRIF对cAMP水平无显著影响，SRIF在1微米以下对腺苷环化酶活性无明显影响。SRIF(100 NM)不改变HIT细胞K~+流出(以86Rb~+表示)。SRIF(高达1微米)对双氧苯酚荧光法测定的膜电位无明显影响。经百日咳毒素(0.1微克/毫升)处理一夜后，SRIF对细胞内钙电流、[Ca~(2+)]i和胰岛素分泌的影响消失，提示SRIF的作用依赖于G蛋白。因此，SRIF减少胰岛素分泌的一个机制是通过电压依赖的钙通道抑制钙内流，这一作用是通过百日咳毒素敏感的G蛋白介导的。
We tested the hypothesis that somatostatin (SRIF) inhibits insulin secretion from an SV40 transformed hamster beta cell line (HIT cells) by an effect on the voltage-dependent Ca2+ channels and examined whether G-proteins were involved in the process. Ca2+ currents were recorded by the whole cell patch-clamp method, the free cytosolic calcium, [Ca2+]i, was monitored in HIT cells by fura-2, and cAMP and insulin secretion were measured by radioimmunoassay. SRIF decreased Ca2+ currents, [Ca2+]i, and basal insulin secretion in a dose-dependent manner over the range of 10(-12)-10(-7)M. The increase in [Ca2+]i and insulin secretion induced by either depolarization with K+ (15 mM) or by the Ca2+ channel agonist, Bay K 8644 (1 microM) was attenuated by SRIF in a dose-dependent manner over the same range of 10(-12)-10(-7) M. the half-maximal inhibitory concentrations (IC50) for SRIF inhibition of insulin secretion were 8.6 X 10(-12) M and 8.3 X 10(-11) M for K+ and Bay K 8644-stimulated secretion and 1 X 10(-10) M and 2.9 X 10(-10) M for the SRIF inhibition of the K+ and Bay K 8644-induced rise in [Ca2+]i, respectively. SRIF also attenuated the rise in [Ca2+]i induced by the cAMP-elevating agent, isobutylmethylxanthine (1 mM) in the presence of glucose. Bay K 8644, K+ and SRIF had no significant effects on cAMP levels and SRIF had no effects on adenylyl cyclase activity at concentrations lower than 1 microM. SRIF (100 nM) did not change K+ efflux (measured by 86Rb+) through ATP-sensitive K+ channels in HIT cells. SRIF (up to 1 microM) had no significant effect on membrane potential measured by bisoxonol fluorescence. Pretreatment of the HIT cells with pertussis toxin (0.1 microgram/ml) overnight abolished the effects of SRIF on Ca2+ currents, [Ca2+]i and insulin secretion implying a G-protein dependence in SRIF's actions. Thus, one mechanism by which SRIF decreases insulin secretion is by inhibiting Ca2+ influx through voltage-dependent Ca2+ channels, an action mediated through a pertussis toxin-sensitive G-protein.