Dick G M, Sturek M
Vascular Biology Laboratory, Dalton Cardiovascular Research Center, University of Missouri, Columbia 65211, USA.
Diabetes. 1996 Jul;45(7):876-80. doi: 10.2337/diab.45.7.876.
The effect of insulin to attenuate the Ca2+ and contractile response of vascular smooth muscle to a number of agonists has been described previously, but the Ca2+ regulatory mechanisms of insulin action remain unclear. We determined the effect of a physiological insulin concentration (300 pmol/l) on the Ca2+ response of vascular smooth muscle cells of the porcine right coronary artery to endothelin 1 (ET-1); furthermore, we examined the cellular Ca2+ stores affected by insulin (i.e., Ca2+ stores releasable by inositol 1,4,5-trisphosphate, caffeine, and ionomycin). We measured the Ca2+ responses of acutely isolated single smooth muscle cells with the fluorescent Ca2+ indicator Fura-2. Acute insulin exposure (20 min) significantly attenuated the Ca2+ response of single smooth muscle cells to 10 nmol/l ET-1. This inhibitory effect of insulin was observed both in the presence and absence of extracellular Ca2+. In contrast with the effects on ET-1-induced Ca2+ responses, insulin did not inhibit the Ca2+ response to 5 mmol/l caffeine, an agent that directly releases sarcoplasmic reticulum Ca2+ stores. Insulin was also without effect on the total cellular Ca2+ store released by 1 micromol/l ionomycin, a Ca2+-transporting ionophore. When ET-1 and caffeine were given in succession, a sizable caffeine-sensitive Ca2+ store could be released from insulin-treated cells but not control cells, indicating that the sarcoplasmic reticulum Ca2+ store of insulin-treated cells was not depleted by ET-1. Generalized depletion of the sarcoplasmic reticulum Ca2+ store is not one of the cellular mechanisms involved in the effect of insulin on coronary smooth muscle; instead, the effect may be due to an inhibitory influence on transmembrane signal transduction, such as diminished ET-1-induced inositol 1,4,5-trisphosphate production or reduced ability of this phosphoinositol to release stored Ca2+.
胰岛素减弱血管平滑肌对多种激动剂的Ca2+和收缩反应的作用此前已有描述，但胰岛素作用的Ca2+调节机制仍不清楚。我们确定了生理浓度胰岛素（300 pmol/l）对猪右冠状动脉血管平滑肌细胞对内皮素1（ET-1）的Ca2+反应的影响；此外，我们研究了受胰岛素影响的细胞Ca2+储存（即可被肌醇1,4,5-三磷酸、咖啡因和离子霉素释放的Ca2+储存）。我们用荧光Ca2+指示剂Fura-2测量急性分离的单个平滑肌细胞的Ca2+反应。急性胰岛素暴露（20分钟）显著减弱了单个平滑肌细胞对10 nmol/l ET-1的Ca2+反应。在有和没有细胞外Ca2+的情况下均观察到胰岛素的这种抑制作用。与对ET-1诱导的Ca2+反应的影响相反，胰岛素不抑制对5 mmol/l咖啡因的Ca2+反应，咖啡因是一种直接释放肌浆网Ca2+储存的试剂。胰岛素对1 μmol/l离子霉素（一种Ca2+转运离子载体）释放的总细胞Ca2+储存也没有影响。当先后给予ET-1和咖啡因时，胰岛素处理的细胞中可释放出相当数量的对咖啡因敏感的Ca2+储存，而对照细胞则不能，这表明胰岛素处理的细胞的肌浆网Ca2+储存未被ET-1耗尽。肌浆网Ca2+储存的普遍耗竭不是胰岛素对冠状动脉平滑肌作用所涉及的细胞机制之一；相反，这种作用可能是由于对跨膜信号转导的抑制性影响，如ET-1诱导的肌醇1,4,5-三磷酸生成减少或该磷酸肌醇释放储存Ca2+的能力降低。
