Ionic basis of cold receptors in cultured sensory cells of rats

当皮肤温度(T)逐渐降低时，冷纤维会引起瞬间的传出放电，引起冷感和获热反应。因此，我们提出冷纤维末端的冷感受器是调节皮肤T抵御寒冷的恒温器。在这里，我们用膜片钳技术研究了培养的大鼠背根神经节(DRG)神经元冷受体的离子基础，作为神经末梢的模型。适度降温后胞浆内钙离子水平升高的细胞被鉴定为具有冷受体的神经元。在这些细胞的全细胞电流钳记录中，冷感受器对降温做出反应，激发动态感受器电位(RP)，短暂地激发冲动。在电压钳记录(-60 mV)中，阶梯冷却引起内向冷流(I(冷))并激活，这是动态RP的基础。从胞外侧进入细胞内的Ca(2)离子可引起细胞失活。反转电位分析表明，I(冷)为非选择性阳离子电流，具有高Ca(2)通透性。冷诱导Ca(2)反应的阈值温度和I(冷)主要在细胞间存在差异。在由外向外的斑块中，当T降低时，单个非选择性阳离子通道在临界T时变得活跃。这意味着冷感受器是一个离子通道，起着最小的恒温器的作用。因为这些热特性与冷纤维中的一致，所以我们认为在神经末梢存在相同的冷受体，并产生冷感觉和冷反应热获得行为的传入冲动。

When temperature (T) of skin decreases stepwise, cold fibers evoke transient efferent discharges, inducing cold sensation and heat-gain responses. Hence we have proposed that cold receptors at distal ends of cold fibers are thermostats to regulate skin T against cold. Here, with patch-clamp techniques, we studied the ionic basis of cold receptors in cultured dorsal root ganglion (DRG) neurons of rats, as a model of nerve endings. Cells that increased cytosolic Ca(2+) level in response to moderate cooling were identified as neurons with cold receptors. In whole-cell current-clamp recordings of these cells, in response to cooling, cold receptors evoked a dynamic receptor potential (RP), eliciting impulses briefly. In voltage-clamp recordings (-60 mV), step cooling induced an inward cold current (I(cold)) with mactivation, underlying the dynamic RP. Ca(2+) ions that entered into cells from extracellular side induced the inactivation. Analysis of the reversal potential implied that I(cold) was nonselective cation current with high Ca(2+) permeability. Threshold temperatures of cooling-induced Ca(2+) response and I(cold) were different primarily among cells. In outside-out patches, when T decreased, single nonselective cation channels became active at a critical T. This implies that a cold receptor is an ion channel and acts as the smallest thermostat. Because these thermal properties were consistent with that in cold fibers, we conclude that the same cold receptors exist at nerve endings and generate afferent impulses for cold sensation and heat-gain behaviors in response to cold.