Ye Q, Heck G L, DeSimone J A
Department of Physiology, Virginia Commonwealth University, Richmond 23298-0551.
J Gen Physiol. 1994 Nov;104(5):885-907. doi: 10.1085/jgp.104.5.885.
Taste sensory responses from the chorda tympani nerve of the rat were recorded with the lingual receptive field under current or voltage clamp. Consistent with previous results (Ye, Q., G. L. Heck, and J. A. DeSimone. 1993. Journal of Neurophysiology. 70:167-178), responses to NaCl were highly sensitive to lingual voltage clamp condition. This can be attributed to changes in the electrochemical driving force for Na+ ions through apical membrane transducer channels in taste cells. In contrast, responses to KCl over the concentration range 50-500 mM were insensitive to the voltage clamp condition of the receptive field. These results indicate the absence of K+ conductances comparable to those for Na+ in the apical membranes of taste cells. This was supported by the strong anion dependence of K salt responses. At zero current clamp, the potassium gluconate (KGlu) threshold was > 250 mM, and onset kinetics were slow (12 s to reach half-maximal response). Faster onset kinetics and larger responses to KGlu occurred at negative voltage clamp (-50 mV). This indicates that when K+ ion is transported as a current, and thereby uncoupled from gluconate mobility, its rate of delivery to the K+ taste transducer increases. Analysis of conductances shows that the paracellular pathway in the lingual epithelium is 28 times more permeable to KCl than to KGlu. Responses to KGlu under negative voltage clamp were not affected by agents that are K+ channel blockers in other systems. The results indicate that K salt taste transduction is under paracellular diffusion control, which limits chemoreception efficiency. We conclude that rat K salt taste occurs by means of a subtight junctional transducer for K+ ions with access limited by anion mobility. The data suggest that this transducer is not cation selective which also accounts for the voltage and amiloride insensitive part of the response to NaCl.
在电流钳或电压钳模式下，记录大鼠鼓索神经的味觉感觉反应，其舌部感受野。与之前的结果一致（Ye, Q., G. L. Heck, and J. A. DeSimone. 1993. Journal of Neurophysiology. 70:167 - 178），对NaCl的反应对舌部电压钳条件高度敏感。这可归因于通过味觉细胞顶端膜换能器通道的Na⁺离子电化学驱动力的变化。相比之下，在50 - 500 mM浓度范围内对KCl的反应对感受野的电压钳条件不敏感。这些结果表明味觉细胞顶端膜中不存在与Na⁺相当的K⁺电导。这得到了K盐反应对阴离子强烈依赖性的支持。在零电流钳时，葡萄糖酸钾（KGlu）阈值> 250 mM，起始动力学缓慢（12秒达到最大反应的一半）。在负电压钳（-50 mV）时，对KGlu的起始动力学更快且反应更大。这表明当K⁺离子作为电流转运，从而与葡萄糖酸根迁移解偶联时，其传递到K⁺味觉换能器的速率增加。电导分析表明，舌上皮中的细胞旁途径对KCl的通透性比对KGlu高28倍。负电压钳下对KGlu的反应不受其他系统中K⁺通道阻滞剂的影响。结果表明K盐味觉转导受细胞旁扩散控制，这限制了化学感受效率。我们得出结论，大鼠K盐味觉是通过一种对K⁺离子的紧密连接下的换能器发生的，其通路受阴离子迁移限制。数据表明这种换能器不是阳离子选择性的，这也解释了对NaCl反应中电压和amiloride不敏感的部分。
