VISUAL TRANSDUCTION IN CONES OF THE MONKEY MACACA-FASCICULARIS
VISUAL TRANSDUCTION IN CONES OF THE MONKEY MACACA-FASCICULARIS
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DOI：
10.1113/jphysiol.1990.sp018193
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发表时间：
1990-08-01
影响因子：
5.5
通讯作者：
BAYLOR, DA
中科院分区：
文献类型：
--
作者：
SCHNAPF, JL;NUNN, BJ;BAYLOR, DA
1.通过测量猕猴视网膜小片投射的单个外节的膜电流，研究了猕猴视锥细胞的视觉传导。2.对短暂的闪光的响应是双相的，类似于峰值频率接近5赫兹的带通滤光器的输出。在暗电流最初减少后，由于开放的光敏通道的数量增加，出现了反弹增加。对光阶跃的响应由一个显著的初始峰值和随后的较小幅度的稳定相位组成。3.对弱光的响应是线性的且不随时间变化，这表明对单个光子的响应是线性相加的。根据闪光灵敏度和有效收集面积，估计了单光子响应的峰值幅度约为30FA。4.随着闪光强度的增加，光电流幅度通常沿着一条比指数关系平缓但比米氏关系陡峭的曲线饱和。在大约650个光致异构化时，响应达到半饱和幅度。5.稳态时的反应-强度关系比开启光阶跃后的短时间更平坦，说明强光延迟了信号转导的减敏作用。这种脱敏并不是由于色素含量的减少。在稳定状态下，强度为I的背景将对弱增量测试闪存的灵敏度降低1/(1+I/IO)，其中IO约为2.6倍。104光异构化S-1，或约3.3LOG的红色和绿色敏感的圆锥体。6.漂白曝光使闪光敏感度永久性降低，但对随后闪光反应的动力学或饱和幅度影响不大。敏感度的降低与视觉色素含量的预期降低一致，并提供了约8倍的光敏性。红色和绿色敏感颜料的10-9µm2(自由溶液值)。在稳定的漂白曝光过程中，光电流的最终指数衰减具有一个速率常数，该速率常数由光强度和光敏度的乘积给出。7.在一些电池中，可以测量到光引起的电流噪声的增加。噪声的功率谱类似于微弱闪光响应的频谱，并且噪声的大小与大小约为20fA的单光子响应一致。8.在黑暗中记录到的膜电流有噪声，在0-20 Hz频段的变化接近0.12 pA_2。暗噪声的功率谱类似于微弱闪光响应的谱。以约2400 S-1的速率发生的光致异构化将产生具有观测到的量级和光谱组成的噪声。
1. Visual transduction in macaque cones was studied by measuring the membrane current of single outer segments projecting from small pieces of retina. 2. The response to a brief flash of light was diphasic and resembled the output of a bandpass filter with a peak frequency near 5 Hz. After the initial reduction in dark current there was a rebound increase which resulted from an increase in the number of open light-sensitive channels. The response to a step of light consisted of a prominent initial peak followed by a steady phase of smaller amplitude. 3. Responses to dim light were linear and time-invariant, suggesting that responses to single photons were linearly additive. From the flash sensitivity and the effective collecting area the peak amplitude of the single photon response was estimated as about 30 fA. 4. With flashes of increasing strength the photocurrent amplitude usually saturated along a curve that was gentler than an exponential but steeper than a Michaelis relation. The response reached the half-saturating amplitude at roughly 650 photoisomerizations. 5. The response-intensity relations was flatter in the steady state than shortly after a light step was turned on, indicating that bright light desensitized the transduction with a delay. This desensitization was not due to a reduction in pigment content. In the steady state, a background of intensity I lowered the sensitivity to a weak incremental test flash by a factor 1/(1 + I/IO), where IO was about 2.6 .times. 104 photoisomerizations s-1, or about 3.3 log trolands for the red- and green-sensitive cones. 6. Bleaching exposures produced permanent reductions in flash sensitivity but had little effect on the kinetics or saturating amplitude of subsequent flash responses. The sensitivity reductions were consistent with the expected reductions in visual pigment content and gave photosensitivities of about 8 .times. 10-9 .mu.m2 (free solution value) for the red- and green-sensitive pigments. During a steady bleaching exposure the final exponential decline of the photocurrent had a rate constant given by the product of the light intensity and the photosensitivity. 7. In some cells it was possible to measure a light-induced increase in current noise. The power spectrum of the noise resembled the spectrum of the dim flash response and the magnitude of the noise was consistent with a single photon response roughly 20 fA in size. 8. The membrane current recorded in darkness was noisy, with a variance near 0.12 pA2 in the band 0-20 Hz. The power spectrum of the dark noise resembled the spectrum of the dim flash response. Noise with the observed magnitude and spectral composition would be generated by photoisomerizations occurring at a rate of abut 2400 s-1.