SPATIAL SPREAD OF ACTIVATION AND BACKGROUND DESENSITIZATION IN TOAD OUTER SEGMENTS
SPATIAL SPREAD OF ACTIVATION AND BACKGROUND DESENSITIZATION IN TOAD OUTER SEGMENTS
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DOI：
10.1113/jphysiol.1981.sp013921
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发表时间：
1981-01-01
影响因子：
5.5
通讯作者：
YAU, KW
中科院分区：
文献类型：
--
作者：
LAMB, TD;MCNAUGHTON, PA;YAU, KW
在离体蟾蜍视网膜上记录单个外节的膜电流，研究视杆细胞激活和背景脱敏的扩散。闪光灯的灵敏度略有变化沿着外段，下降了约30%，从基地到尖端。当仅外节的远侧半部分在记录移液管中时，未记录部分的照明在记录部分引起很少或没有光电流，表明光敏化不会引起整个外节的激活。与漫射照明的外部部分完全吸入吸管，在固定的时间的强度响应关系是不变的形式为大多数的闪光响应的上升阶段，并大大陡峭比米氏关系。所观察到的关系是一致的模型，其中光异构化块的外段的一个短区域的所有通道。由于照明被限制在一个狭窄的横向狭缝中，在固定时间的强度-响应关系就没有那么陡峭了，这是因为激活的纵向扩展非常有限。内部发射器的有效纵向扩散系数的上限约为3 × 10 - 4。10-7 cm 2/s。这对应于发射机纵向扩展的空间常数aptx。在暗淡响应峰值时为3 μ m。闪光反应的时间过程中引起的光定位在边缘或中心的外段是非常相似的。横向狭缝稳定照射引起的减敏也被纵向定位。线性减敏参数（T），在光异构化位点的任一侧上沿着外段近似指数地沿着衰减，空间常数为apx。6时横向扩散脱敏效果优于纵向扩散。在关闭昏暗的漫射背景光后，T的衰减大致呈指数关系，时间常数为几秒。这和6 μ m的稳态空间常数表明，减感物质的有效纵向扩散系数为apx。10-7 cm 2/s。激活和脱敏的受限纵向扩散可以通过外节中堆叠的膜盘呈现的扩散屏障来解释。这种阻挡作用使有效纵向扩散系数降低到普通水扩散系数的约1/50，但对横向扩散没有显著影响。
The spread of activation and background desensitization in rods was studied by recording membrane current from single outer segments in pieces of isolated toad retina. Flash sensitivity changed slightly along the outer segment, falling by about 30% from base to tip. When only the distal half of an outer segment was in the recording pipette, illumination of the unrecorded part elicited little or no photocurrent at the recorded part, indicating that a photosensitization does not cause activation of the entire outer segment. With diffuse illumination of an outer segment fully drawn into the pipette, the intensity-response relations at fixed times were invariant in form for most of the rising phase of the flash response and were considerably steeper than the Michaelis relation. The observed relation was consistent with a model in which a photoisomerization blocks all channels over a short region of the outer segment. With illumination restricted to a narrow transverse slit, the intensity-response relations at fixed times were much less steep, as would be expected for a very limited longitudinal spread of activation. An upper limit for the effective longitudinal diffusion coefficient of the internal transmitter was about 3 .times. 10-7 cm2/s. This corresponds to a space constant for longitudinal spread of transmitter of .apprx. 3 .mu.m at the time of the dim response peak. The time course of flash responses elicited with light positioned either on the edge or on the center of the outer segment was very similar. Desensitization resulting from steady illumination by a transverse slit was also localized longitudinally. A linear desensitization parameter (T), decayed approximately exponentially along the outer segment, on either side of the site of photoisomerization, with a space constant of .apprx. 6 .mu.m. Transverse spread of desensitization was more effective than longitudinal spread. After turning off a dim diffuse background light, the decay of T was roughly exponential with a time constant of several s. This and the steady state space constant of 6 .mu.m show that the effective longitudinal diffusion coefficient for a desensitizing substance is .apprx. 10-7 cm2/s. The restricted longitudinal spread of activation and desensitization may be explained by the barrier to diffusion presented by the stacked membranous discs in the outer segment. This baffling reduces the effective longitudinal diffusion coefficient to about 1/50 that or ordinary aqueous diffusion, but it does not significantly affect transverse spread.