Carmines P K, Ohishi K, Ikenaga H
Department of Physiology and Biophysics, University of Nebraska Medical Center, Omaha 68198-4575, USA.
J Clin Invest. 1996 Dec 1;98(11):2564-71. doi: 10.1172/JCI119075.
Experiments were performed to test the hypothesis that diabetes mellitus is associated with impaired afferent arteriolar responsiveness to opening of voltage-gated calcium channels. Diabetes was induced by injection of streptozocin (65 mg/kg, i.v.) and insulin was administered via an osmotic minipump to achieve moderate hyperglycemia. Sham rats received vehicle treatments. 2 wk later, the in vitro blood-perfused juxtamedullary nephron technique was used to allow videomicroscopic measurement of afferent arteriolar contractile responses to increasing bath concentrations of either Bay K 8644 or K+. Baseline afferent arteriolar diameter in kidneys from diabetic rats (26.4+/-1.2 microm) exceeded that of Sham rats (19.7+/-1.0 microm). Bay K 8644 evoked concentration-dependent reductions in afferent diameter in both groups of kidneys; however, arterioles from Sham rats responded to 1 nM Bay K 8644 while 100 nM Bay K 8644 was required to contract arterioles from diabetic rats. The EC50 for K+-induced reductions in afferent arteriolar diameter was greater in diabetic kidneys (40+/-4 mM) than in kidneys from Sham rats (28+/-4 mM; P < 0.05). In afferent arterioles isolated by microdissection from Sham rats and loaded with fura 2, increasing bath [K+] from 5 to 40 mM evoked a 98+/-12 nM increase in intracellular Ca2+ concentration ([Ca2+]i). [Ca2+]i responses to 40 mM K+ were suppressed in afferent arterioles from diabetic rats (delta = 63+/-5 nM), but were normalized by decreasing bath glucose concentration from 20 to 5 mM. These observations indicate that the early stage of insulin-dependent diabetes mellitus is associated with a functional defect in afferent arteriolar L-type calcium channels, an effect which may contribute to suppressed afferent arteriolar vasoconstrictor responsiveness and promote glomerular hyperfiltration.
进行实验以检验糖尿病与入球小动脉对电压门控钙通道开放的反应性受损有关这一假说。通过静脉注射链脲佐菌素（65mg/kg）诱导糖尿病，并通过渗透微型泵给予胰岛素以实现中度高血糖。假手术大鼠接受载体处理。2周后，采用体外血液灌注近髓肾单位技术，通过视频显微镜测量入球小动脉对浴液中Bay K 8644或K+浓度增加的收缩反应。糖尿病大鼠肾脏的入球小动脉基线直径（26.4±1.2μm）超过假手术大鼠（19.7±1.0μm）。Bay K 8644在两组肾脏中均引起入球小动脉直径的浓度依赖性降低；然而，假手术大鼠的小动脉对1nM Bay K 8644有反应，而糖尿病大鼠的小动脉需要100nM Bay K 8644才能收缩。K+诱导的入球小动脉直径降低的EC50在糖尿病肾脏中（40±4mM）大于假手术大鼠的肾脏（28±4mM；P<0.05）。从假手术大鼠中通过显微解剖分离并加载fura 2的入球小动脉中，浴液[K+]从5mM增加到40mM可引起细胞内Ca2+浓度（[Ca2+]i）增加98±12nM。糖尿病大鼠入球小动脉对40mM K+的[Ca2+]i反应受到抑制（Δ=63±5nM），但通过将浴液葡萄糖浓度从20mM降低到5mM可使其恢复正常。这些观察结果表明，胰岛素依赖型糖尿病的早期阶段与入球小动脉L型钙通道的功能缺陷有关，这一效应可能导致入球小动脉血管收缩反应性受到抑制，并促进肾小球超滤。
