Cyclic AMP diffusion coefficient in frog olfactory cilia
Cyclic AMP diffusion coefficient in frog olfactory cilia
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DOI：
10.1016/s0006-3495(99)77440-0
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发表时间：
1999-05-01
影响因子：
3.4
通讯作者：
Koutalos, Y
中科院分区：
文献类型：
--
作者：
Chen, CH;Nakamura, T;Koutalos, Y
环磷酸腺苷（cAMP）是脊椎动物嗅纤毛中介导气味信号转导的细胞内信使之一。因此，cAMP在嗅纤毛中的扩散系数是嗅觉信号传导的重要因素。本文用离体的尖音蛙纤毛标本测定了cAMP的扩散系数。在这种制备中，将嗅纤毛吸入贴片吸管中，并在纤毛的基部形成千兆密封。随后，切除纤毛，使浴cAMP扩散到纤毛中并激活质膜上的环核苷酸门控通道。为了估计cAMP的扩散系数，我们分析了在不存在cAMP水解的情况下，浴中cAMP浓度的阶跃变化引起的电流的动力学。在这样的条件下，cAMP激活电流的动力学具有对扩散系数的简单依赖性。从分析中，我们得到cAMP扩散系数为2.7 +/- 0.2。10（-6）cm（2）s（-1）。该值与水溶液中的预期值相似，表明嗅纤毛内没有明显的扩散屏障。在cAMP浓度高于5 μ M，扩散大大减慢，这表明存在缓冲的固定cAMP结合位点。这种缓冲部位的一个合理的生理功能是延长细胞对强刺激的反应。
Cyclic AMP (cAMP) is one of the intracellular messengers that mediate odorant signal transduction in vertebrate olfactory cilia. Therefore, the diffusion coefficient of cAMP in olfactory cilia is an important factor in the transduction of the odorous signal. We have employed the excised cilium preparation from the grass frog (Rana pipiens) to measure the cAMP diffusion coefficient. In this preparation an olfactory cilium is drawn into a patch pipette and a gigaseal is formed at the base of the cilium. Subsequently the cilium is excised, allowing bath cAMP to diffuse into the cilium and activate the cyclic nucleotide-gated channels on the plasma membrane. In order to estimate the cAMP diffusion coefficient, we analyzed the kinetics of the currents elicited by step changes in the bath cAMP concentration in the absence of cAMP hydrolysis. Under such conditions, the kinetics of the cAMP-activated currents has a simple dependence on the diffusion coefficient. From the analysis we have obtained a cAMP diffusion coefficient of 2.7 +/- 0.2 . 10(-6) cm(2) s(-1) for frog olfactory cilia. This Value is similar to the expected value in aqueous solution, suggesting that there are no significant diffusional barriers inside olfactory cilia. At cAMP concentrations higher than 5 mu M, diffusion slowed considerably, suggesting the presence of buffering by immobile cAMP binding sites. A plausible physiological function of such buffering sites would be to prolong the response of the cell to strong stimuli.