COMPETITIVE-INHIBITION OF THE RESPONSE TO NA+ BY CA2+ IN WATER FIBERS OF THE FROG GLOSSOPHARYNGEAL NERVE
COMPETITIVE-INHIBITION OF THE RESPONSE TO NA+ BY CA2+ IN WATER FIBERS OF THE FROG GLOSSOPHARYNGEAL NERVE
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DOI：
10.1093/chemse/16.1.95
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发表时间：
1991-02-01
期刊：
影响因子：
3.5
通讯作者：
KITADA, Y
中科院分区：
文献类型：
--
作者：
KITADA, Y
青蛙舌咽神经的单水纤维对低浓度的 CaCl2 (1-2 mM) 和相对高浓度的 NaCl (> 80 mM) 有反应。 然而，低浓度 CaCl2 和相对高浓度 NaCl 的混合物刺激仅产生很小的反应，表明 Ca2+ 和 Na+ 的作用是相互拮抗的。 据报道，Na+ 通过与 Ca2+ 竞争钙受体位点来抑制对 Ca2+ 的反应（X(Ca)；Kitada 和 Shimada，1980）。 在本研究中，发现Ca2+抑制对Na+的反应。 因此，负责对 Na+ 做出反应的钠受体位点 (X(Na)) 与 X(Ca) 不同。 定量研究了 Ca2+ 对 Na+ 反应的抑制，假设神经反应的强度与 NaX(Na) 复合物的量减去常数（NaX(Na) 复合物的阈值浓度）成正比。 所得结果表明Ca2+与Na+竞争X(Na)。 本研究获得的NaX(Na)配合物和CaX(Na)配合物的表观解离常数分别为1.0 M和1.2 x 10(-3) M。 正如此处提出的，X(Na) 并不简单地代表阳离子的结合位点，因为可能存在拮抗阳离子对 X(Na) 的竞争。 X(Na)对Ca2+的高亲和力表明X(Na)是参与盐味接收的特定受体位点。 由于 Mg2+ 不影响对 Na+ 的响应，因此 X(Na) 对阳离子的亲和力不是电荷特异性的，而是化学特异性的。 目前的结果表明，Ca2+和Na+在青蛙舌咽神经的水纤维中具有双重作用，既参与兴奋又参与抑制。
Single water fibers of the frog glossopharyngeal nerve respond to low concentrations of CaCl2 (1-2 mM) and to relatively high concentrations of NaCl (> 80 mM). However, stimulation by a mixture with a low concentration of CaCl2 and relatively high concentration of NaCl gives rise to only a small response, suggesting that the effects of Ca2+ and Na+ are mutually antagonistic. It has been reported that Na+ inhibits the response to Ca2+ by competing with Ca2+ for a calcium receptor site (X(Ca); Kitada and Shimada, 1980). In the present study, it was found that Ca2+ inhibited the response to Na+. Therefore, the sodium receptor site (X(Na)) responsible for the response to Na+ is different from X(Ca). The inhibition of the response to Na+ by Ca2+ was examined quantitatively on the assumption that the magnitude of the neural response is proportional to the amount of NaX(Na) complex minus a constant (the threshold concentration of the NaX(Na) complex). The results obtained indicate that Ca2+ competes with Na+ for X(Na). The apparent dissociation constants for the NaX(Na) complex and the CaX(Na) complex obtained from the present study were 1.0 M and 1.2 x 10(-3) M, respectively. X(Na), as proposed here, does not represent simply a binding site for cations since there can be competition for X(Na) by an antagonistic cation. The high affinity of X(Na) for Ca2+ suggests that X(Na) is a specific receptor site involved in salt-taste reception. Since Mg2+ did not affect the response to Na+, the affinity of X(Na) for cations is not charge-specific but is, rather, chemically specific. The present results indicate that both Ca2+ and Na+ have a dual action, being involved both in excitation and in inhibition, in water fibers of the frog glossopharyngeal nerve.