CYTOPLASMIC CALCIUM AS THE MESSENGER FOR LIGHT ADAPTATION IN SALAMANDER RODS
CYTOPLASMIC CALCIUM AS THE MESSENGER FOR LIGHT ADAPTATION IN SALAMANDER RODS
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DOI：
10.1113/jphysiol.1989.sp017757
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发表时间：
1989-09-01
影响因子：
5.5
通讯作者：
MURPHY, RLW
中科院分区：
文献类型：
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作者：
FAIN, GL;LAMB, TD;MURPHY, RLW
1. 为了研究细胞质钙浓度（Ca2+i）在杆状光感受器光适应中的作用，我们试图通过最小化通过外段质膜的钙通量来防止光诱导的Ca2+i变化。这是通过将外段暴露于低钙离子，0 - Na+溶液中实现的，其中钠被胍或锂取代，外部钙浓度（Ca2+o）降低到微摩尔水平。2. 使用胍和1‐3 microM‐Ca2+o，黑暗中的循环电流维持了至少15 s，与Ca2+i的近似稳定性一致。使用Li+而不是胍时，大部分初始电流被抑制，但剩余电流仍然相对稳定。3. 在低- Ca2+， 0 - Na+溶液中长时间暴露（大于30秒），然后在昏暗的照明下，循环电流不保持恒定，而是缓慢增加。将钙缓冲液掺入细胞质大大降低了电流的变化率，这与Ca2+i逐渐减少导致电流增加的观点一致。4. 在黑暗中暴露于低Ca2+， 0‐Na+溶液的杆的光响应以一种特有的方式改变。虽然光响应的初始上升相位变化不大，但响应的峰值幅度更大，发生时间更晚，响应衰减速度比对照组慢。对于闪光和光阶，响应强度关系变陡，并向较低强度方向移动。阶跃响应的正常垂度消失，阶跃响应的波形可以由微弱闪光响应的积分近似预测。5. 在林格溶液中呈现背景照明，对随后的明亮闪光的反应明显加速。如果背景是在低Ca2+， 0‐Na+溶液中，则没有观察到这种加速。6. 第4段和第5段描述的结果表明，在Ca2+i变化最小的条件下，所有光适应的表现都消失了，杆只是以不变的积分时间求和入射光子的影响。7. 将光适应棒暴露在低Ca2+， 0‐Na+溶液中，会改变对叠加测试闪光的反应，其方式与在黑暗中棒的反应大致相同。在低Ca2+， 0‐Na+溶液中，初始上升相没有变化，但响应更大，峰值更晚，衰减更慢。（摘要删节为400字）
1. In order to study the role of cytoplasmic calcium concentration (Ca2+i) in rod photoreceptor light adaptation, we have attempted to prevent light‐induced changes in Ca2+i by minimizing calcium fluxes across the outer segment plasma membrane. This was achieved by exposing the outer segment to a low‐Ca2+, 0‐Na+ solution, in which sodium was replaced with either guanidinium or lithium and the external calcium concentration (Ca2+o) was reduced to micromolar levels. 2. With guanidinium and 1‐3 microM‐Ca2+o, the circulating current in darkness was maintained for a period of at least 15 s, consistent with approximate stability of Ca2+i. With Li+ rather than guanidinium most of the initial current was suppressed, but the residual current was again relatively stable. 3. During prolonged exposures (greater than 30 s) to low‐Ca2+, 0‐Na+ solution followed by dim illumination, the circulating current did not remain constant but slowly increased. Incorporation of calcium buffer into the cytoplasm greatly reduced the rate of change of current, consistent with the idea that the increase arose from a gradual decrease in Ca2+i. 4. Light responses of rods exposed to low‐Ca2+, 0‐Na+ solution in darkness were altered in a characteristic manner. Although the initial rising phase of the light response was little changed, the peak amplitude of the response was larger and occurred later, and the response decayed more slowly than in control. The response‐intensity relation was steepened and was shifted towards lower intensities both for flashes and for steps of light. The normal sag in the response to steps disappeared, and the waveform of the step response could be predicted to a close approximation from the integral of the dim flash response. 5. Presentation of background illumination in Ringer solution produced a marked acceleration of the response to a subsequent bright flash. No such acceleration was observed if the background was given in low‐Ca2+, 0‐Na+ solution. 6. The results described in paragraphs 4 and 5 indicate that, under conditions expected to minimize changes in Ca2+i, all manifestations of light adaptation disappear, and the rod simply sums the effects of incident photons with an invariant integration time. 7. Exposure of a light‐adapted rod to low‐Ca2+, 0‐Na+ solution altered the responses to superimposed test flashes in much the same way as for rods in darkness. The initial rising phases in low‐Ca2+, 0‐Na+ solution were unchanged, but the responses were larger, reached peak later and decayed more slowly.(ABSTRACT TRUNCATED AT 400 WORDS)