Brock James, Acosta M Carmen, Al Abed Amr, Pianova Svetlana, Belmonte Carlos
Prince of Wales Medical Research Institute, Barker St, Randwick, NSW 2031, Australia.
J Physiol. 2006 Sep 1;575(Pt 2):573-81. doi: 10.1113/jphysiol.2006.110130. Epub 2006 Jun 22.
An in vitro preparation of the guinea-pig cornea was used to study the effects of the K+ channel blockers 4-aminopyridine (4-AP), tetraethylammonium (TEA) and Ba2+ on nerve terminal impulses (NTIs) recorded extracellularly from cold sensory receptors. These receptors have an ongoing discharge of NTIs that is increased by cooling and decreased by heating. The K+ channel blocker 4-AP reduced the negative amplitude of the diphasic (positive-negative) NTIs, whereas TEA and Ba2+ prolonged the duration of the negative component. As the shape of the NTI is determined by the first derivative (dV/dt) of the membrane voltage change, these changes in the negative component are consistent with the blockade of K+ channels that contribute to action potential repolarization. Only TEA changed the basal activity of the receptors, increasing the likelihood of burst discharges. Ba2+ selectively reduced the response of the receptors to heating, whereas neither 4-AP nor TEA modified the response to heating or to cooling. The findings indicate that K+ channels blocked by 4-AP, TEA and Ba2+ contribute to action potential repolarization in corneal cold receptors, and that ionic mechanisms that underlie the reduction in NTI frequency in response to heating differ from those that increase activity in response to cooling.
利用豚鼠角膜的体外制备物，研究钾离子通道阻滞剂4-氨基吡啶（4-AP）、四乙铵（TEA）和钡离子（Ba2+）对从冷觉感受器细胞外记录的神经末梢冲动（NTIs）的影响。这些感受器持续发放NTIs，冷却时发放增加，加热时发放减少。钾离子通道阻滞剂4-AP降低了双相（正负）NTIs的负向幅度，而TEA和Ba2+延长了负向成分的持续时间。由于NTI的形状由膜电压变化的一阶导数（dV/dt）决定，负向成分的这些变化与参与动作电位复极化的钾离子通道被阻断一致。只有TEA改变了感受器的基础活动，增加了爆发性放电的可能性。Ba2+选择性地降低了感受器对加热的反应，而4-AP和TEA都没有改变对加热或冷却的反应。这些发现表明，被4-AP、TEA和Ba2+阻断的钾离子通道参与角膜冷觉感受器的动作电位复极化，并且响应加热时NTI频率降低和响应冷却时活动增加的离子机制不同。
