先天性静止性夜盲大鼠视杆双极细胞L-钙通道电生理特征

Electrophysiology properties of L-type calcium channel in rod bipolar cells of CSNB rat

目的研究先天性静止性夜盲(CSNB)大鼠视杆双极细胞(RBCs)L-钙通道的生理学特征,探讨其与视觉信号传导通路障碍的关系。方法选取4～8周龄SD大鼠20只(对照组)、CSNB大鼠23只(实验组),深度麻醉后处死大鼠,制作视网膜切片,红外显微镜下寻找RBCs胞体,运用全细胞膜片钳模式记录L-钙通道电流,并记录程序刺激后细胞静息膜电容(restCm)的变化值(△Cm),计算胞吐系数(EI)。结果对照组L-钙通道电流于-20～-30mV达到峰值(-33.2±2.5)pA,实验组电流于-15mV左右达峰值,为(12.2±2.3)pA;L-钙通道特异性阻断剂nifedipine(10μm)可以完全阻断所记录的钙电流。GABA受体阻断剂PTX(100μm)能够明显阻断实验组除极时诱发的外向电流。与对照组比较,实验组的△Cm和EI均明显降低(P<0.01)。结论 CSNB大鼠双极细胞L-钙通道电生理特征的改变会严重影响其向下级神经元释放神经递质,这可能是导致CSNB发病的机制之一。

BackgroundThe L-type calcium channel encoded by Cacnalf gene has been considered as a key point in triggering off neurotransmitter vesicular release of retinal neuron.The dysfunction of L-type calcium channel might cause disturbances of retinal signal transmission.ObjectiveThe present study was to investigate the properties of L-type calcium current of rod bipolar cells in congenital stationary night blindness（CSNB）rat.MethodsThe retinal slices prepared from 23 CSNB rats and 20 SD rats（as control）were used for patch clamp recording.According to the reference,rod bipolar cells from 200μm retinal vertical slice were identified and selected under the infra-red differential interference microscope and formed a tight-seal whole-cell recording configuration for calcium channel current recording using patch clamp technique.Resting membrane capacitance（restCm）and the increase of restCm（△Cm）after protocol activation were obtained for the calculation of the exocytotic index（EI）based on the formula：EI= △Cm/restCm×100.ResultsThe peak L-type calcium current was recorded between the-20 and-30mV in SD rats with the average amplitude of（-33.2±2.5）pA,whereas that of CSNB rats was around-15mV with the mean value of（12.2±2.3）pA during ramp depolarizing.The L-type calcium currents of both SD and SCNB rats were completely blocked by low concentration of nifedipine（10μm）.Outward currents overlaying on calcium current during depolarization were observed in SD rats,and these currents were effectively eliminated by GABA-receptor blocker PTX（100μm）.Compared with SD rats,the △Cm and EI were significantly lower in CSNB rats（P0.01）.ConclusionThe alterations of L-type calcium channel property in rod bipolar cell of CSNB lead to disruption of neurotransmitter release and visual signal transmission,which might be one of pathophysiological mechanisms for CSNB.