Zawalich W S, Bonnet-Eymard M, Zawalich K C
Yale University School of Nursing, New Haven, CT 06536-0740, USA.
Metabolism. 2000 Sep;49(9):1156-63. doi: 10.1053/meta.2000.8613.
During a dynamic perifusion, 20 mmol/L glucose, 20 mmol/L alpha-ketoisocaproate (KIC) or 20 mmol/L methyl pyruvate (MP) stimulate biphasic insulin secretory responses from collagenase-isolated rat islets. Peak first-phase insulin responses were comparable for all 3 nutrient agonists. The largest second-phase insulin secretory response was evoked by 20 mmol/L glucose (30-fold above basal release rates), and this response was more sustained than that observed with either 20 mmol/L KIC or 20 mmol/L MP. When mouse islets were perifused under similar conditions, KIC stimulated the largest first-phase insulin response, while comparable acute insulin secretion rates were obtained with glucose- or MP-stimulated islets. In contrast to rat islets, the sustained second phase of insulin secretion from mouse islets was minimal regardless of the nutrient secretagogue used. This anomalous response of mouse islets as compared with rat islets could not be ascribed to any obvious difference in the glucose usage rate or insulin content between these 2 species. Glucose, KIC, or MP stimulated significant increases in 3H-inositol phosphates in rat islets. Significantly smaller increases were measured in mouse islets. Comparative Western blot analyses showed pronounced species differences in the expression of phospholipase Cbeta1 (PLCbeta1), PLCbeta2, PLCbeta3, and PLCdelta1 but not PLCgamma1 or protein kinase Calpha (PKCalpha) between rat and mouse islets. PLCbeta4 or PLCdelta2 could not be identified in either species. These findings are consistent with the concept that the underexpression of the nutrient-activated PLC isozyme may account for the minimal inositol phosphate (IP) and second-phase insulin secretory response from mouse islets.
在动态灌流过程中，20 mmol/L葡萄糖、20 mmol/Lα-酮异己酸（KIC）或20 mmol/L丙酮酸甲酯（MP）可刺激胶原酶分离的大鼠胰岛产生双相胰岛素分泌反应。所有3种营养激动剂的第一相胰岛素反应峰值相当。20 mmol/L葡萄糖引发的第二相胰岛素分泌反应最大（比基础释放速率高30倍），且该反应比20 mmol/L KIC或20 mmol/L MP所观察到的反应更持久。当在相似条件下对小鼠胰岛进行灌流时，KIC刺激的第一相胰岛素反应最大，而葡萄糖或MP刺激的胰岛获得的急性胰岛素分泌速率相当。与大鼠胰岛不同，无论使用何种营养促分泌剂，小鼠胰岛胰岛素分泌的持续第二相都很微弱。与大鼠胰岛相比，小鼠胰岛的这种异常反应不能归因于这两个物种在葡萄糖利用率或胰岛素含量上的任何明显差异。葡萄糖、KIC或MP可刺激大鼠胰岛中3H-肌醇磷酸显著增加。在小鼠胰岛中测得的增加量明显较小。比较蛋白质印迹分析显示，大鼠和小鼠胰岛在磷脂酶Cβ1（PLCβ1）、PLCβ2、PLCβ3和PLCδ1的表达上存在明显的物种差异，但在PLCγ1或蛋白激酶Cα（PKCα）方面没有差异。在这两个物种中均未鉴定出PLCβ4或PLCδ2。这些发现与以下概念一致，即营养激活的PLC同工酶表达不足可能是小鼠胰岛中肌醇磷酸（IP）和第二相胰岛素分泌反应微弱的原因。
