Painful diabetic neuropathy occurs in approximately 20% of diabetic patients with underlying pathomechanisms not fully understood. We evaluated the contribution of the Ca_V3.2 isoform of T-type calcium channel to hyperglycemia-induced changes in cutaneous sensory C-fiber functions and neuropeptide release employing the streptozotocin (STZ) diabetes model in congenic mouse strains including global knockouts (KOs). Hyperglycemia established for 3–5 weeks in male C57BL/6J mice led to major reorganizations in peripheral C-fiber functions. Unbiased electrophysiological screening of mechanosensitive single-fibers in isolated hairy hindpaw skin revealed a relative loss of (polymodal) heat sensing in favor of cold sensing. In healthy Ca_V3.2 KO mice both heat and cold sensitivity among the C-fibers seemed underrepresented in favor of exclusive mechanosensitivity, low-threshold in particular, which deficit became significant in the diabetic KOs. Diabetes also led to a marked increase in the incidence of spontaneous discharge activity among the C-fibers of wildtype mice, which was reduced by the specific Ca_V3.2 blocker TTA-P2 and largely absent in the KOs. Evaluation restricted to the peptidergic class of nerve fibers - measuring KCl-stimulated CGRP release - revealed a marked reduction in the sciatic nerve by TTA-P2 in healthy but not diabetic wildtypes, the latter showing CGRP release that was as much reduced as in healthy and, to the same extent, in diabetic Ca_V3.2 KOs. These data suggest that diabetes abrogates all Ca_V3.2 functionality in the peripheral nerve axons. In striking contrast, diabetes markedly increased the KCl-stimulated CGRP release from isolated hairy skin of wildtypes but not KO mice, and TTA-P2 reversed this increase, strongly suggesting a de novo expression of Ca_V3.2 in peptidergic cutaneous nerve endings which may contribute to the enhanced spontaneous activity. De-glycosylation by neuraminidase showed clear desensitizing effects, both in regard to spontaneous activity and stimulated CGRP release, but included actions independent of Ca_V3.2. However, as diabetes-enhanced glycosylation is decisive for intra-axonal trafficking, it may account for the substantial reorganizations of the Ca_V3.2 distribution. The results may strengthen the validation of Ca_V3.2 channel as a therapeutic target of treating painful diabetic neuropathy.

大约 20% 的糖尿病患者会出现疼痛性糖尿病性神经病变，其潜在的病理机制尚不完全清楚。我们评估了 T 型钙通道的 Ca _V 3.2 亚型对高血糖引起的皮肤感觉 C 纤维功能变化和神经肽释放的贡献，采用链脲佐菌素 (STZ) 糖尿病模型，包括全局基因敲除 (KO)。在雄性 C57BL/6J 小鼠中建立 3-5 周的高血糖导致外周 C 纤维功能的重大重组。对分离的多毛后爪皮肤中的机械敏感单纤维进行的无偏电生理学筛选显示，（多峰）热感应的相对损失有利于冷感应。在健康的 Ca _V3.2 KO 小鼠的 C 纤维之间的热敏感性和冷敏感性似乎没有得到充分体现，有利于独有的机械敏感性，尤其是低阈值，这种缺陷在糖尿病 KO 中变得很明显。糖尿病还导致野生型小鼠 C 纤维中自发放电活动的发生率显着增加，而特定的 Ca _V 3.2 阻滞剂 TTA-P2 减少了这种活动，并且在 KO 中基本不存在。仅限于肽能类神经纤维的评估 - 测量氯化钾刺激的 CGRP 释放 - 显示 TTA-P2 在健康而非糖尿病野生型中显着减少坐骨神经，后者显示 CGRP 释放与健康和糖尿病中一样减少, 在相同程度上, 在糖尿病 Ca _V3.2 击倒。这些数据表明糖尿病消除了周围神经轴突中的所有 Ca _V 3.2 功能。形成鲜明对比的是，糖尿病显着增加了野生型毛茸茸皮肤中 KCl 刺激的 CGRP 释放，但 KO 小鼠没有，TTA-P2 逆转了这种增加，强烈表明 Ca _V 3.2 在肽能皮肤神经末梢的重新表达可能有助于到增强的自发活动。神经氨酸酶的去糖基化作用在自发活动和刺激的 CGRP 释放方面显示出明显的脱敏作用，但包括独立于 Ca _V 3.2 的作用。然而，由于糖尿病增强的糖基化对轴突内运输具有决定性作用，它可能解释了 Ca 的大量重组_V 3.2 分布。该结果可能会加强 Ca _V 3.2 通道作为治疗疼痛性糖尿病性神经病变的治疗靶点的有效性。