Lu Zhongju, Jiang Ya-Ping, Xu Xin-Hua, Ballou Lisa M, Cohen Ira S, Lin Richard Z
Department of Physiology and Biophysics and the Institute of Molecular Cardiology, Stony Brook University, Stony Brook, New York 11794-8151, USA.
Diabetes. 2007 Nov;56(11):2780-9. doi: 10.2337/db06-1629. Epub 2007 Jul 31.
Contraction of cardiac myocytes is initiated by Ca(2+) entry through the voltage-dependent L-type Ca(2+) channel (LTCC). Previous studies have shown that phosphatidylinositol (PI) 3-kinase signaling modulates LTCC function. Because PI 3-kinases are key mediators of insulin action, we investigated whether LTCC function is affected in diabetic animals due to reduced PI 3-kinase signaling.
We used whole-cell patch clamping and biochemical assays to compare cardiac LTCC function and PI 3-kinase signaling in insulin-deficient diabetic mice heterozygous for the Ins2(Akita) mutation versus nondiabetic littermates.
Diabetic mice had a cardiac contractility defect, reduced PI 3-kinase signaling in the heart, and decreased L-type Ca(2+) current (I(Ca,L)) density in myocytes compared with control nondiabetic littermates. The lower I(Ca,L) density in myocytes from diabetic mice is due at least in part to reduced cell surface expression of the LTCC. I(Ca,L) density in myocytes from diabetic mice was increased to control levels by insulin treatment or intracellular infusion of PI 3,4,5-trisphosphate [PI(3,4,5)P(3)]. This stimulatory effect was blocked by taxol, suggesting that PI(3,4,5)P(3) stimulates microtubule-dependent trafficking of the LTCC to the cell surface. The voltage dependence of steady-state activation and inactivation of I(Ca,L) was also shifted to more positive potentials in myocytes from diabetic versus nondiabetic animals. PI(3,4,5)P(3) infusion eliminated only the difference in voltage dependence of steady-state inactivation of I(Ca,L).
Decreased PI 3-kinase signaling in myocytes from type 1 diabetic mice leads to reduced Ca(2+) entry through the LTCC, which might contribute to the negative effect of diabetes on cardiac contractility.
心肌细胞的收缩由通过电压依赖性L型钙通道（LTCC）的Ca(2+)内流引发。先前的研究表明，磷脂酰肌醇（PI）3-激酶信号传导可调节LTCC功能。由于PI 3-激酶是胰岛素作用的关键介质，我们研究了在糖尿病动物中，LTCC功能是否因PI 3-激酶信号传导减少而受到影响。
我们使用全细胞膜片钳技术和生化分析方法，比较了Ins2(Akita)突变杂合的胰岛素缺乏型糖尿病小鼠与非糖尿病同窝小鼠的心脏LTCC功能和PI 3-激酶信号传导。
与对照非糖尿病同窝小鼠相比，糖尿病小鼠存在心脏收缩功能缺陷、心脏中PI 3-激酶信号传导减少以及心肌细胞中L型钙电流（I(Ca,L)）密度降低。糖尿病小鼠心肌细胞中较低的I(Ca,L)密度至少部分归因于LTCC细胞表面表达的减少。通过胰岛素治疗或细胞内注入PI 3,4,5-三磷酸[PI(3,4,5)P(3)]，糖尿病小鼠心肌细胞中的I(Ca,L)密度增加至对照水平。这种刺激作用被紫杉醇阻断，表明PI(3,4,5)P(3)刺激LTCC依赖微管的向细胞表面运输。与非糖尿病动物相比，糖尿病动物心肌细胞中I(Ca,L)的稳态激活和失活的电压依赖性也向更正的电位偏移。PI(3,4,5)P(3)注入仅消除了I(Ca,L)稳态失活电压依赖性的差异。
1型糖尿病小鼠心肌细胞中PI 3-激酶信号传导减少导致通过LTCC的Ca(2+)内流减少，这可能是糖尿病对心脏收缩产生负面影响的原因。
