Role of calcium in regulating the cyclic GMP cascade of phototransduction in retinal rods.
Role of calcium in regulating the cyclic GMP cascade of phototransduction in retinal rods.
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钙在调节视网膜视杆光转导环 GMP 级联中的作用。
DOI：
10.1073/pnas.83.18.7109
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发表时间：
1986
影响因子：
11.1
通讯作者：
Lamb,TD
中科院分区：
文献类型：
--
作者：
Torre,V;Matthews,HR;Lamb,TD
cGMP 和 Ca2+ 似乎都参与了脊椎动物视杆细胞的光转导过程，但它们的确切作用一直存在争议。为了研究 Ca2+ 的作用，我们通过使用贴片移液管将钙缓冲剂 1,2-双（邻氨基苯氧基）乙烷-N,N,N',N'-四乙酸 (BAPTA) 掺入杆细胞质中，人为地增加了杆的钙缓冲能力。在存在缓冲剂的情况下，Na+-Ca2+交换电流大大减慢，表明细胞质钙浓度(Cai)确实已被显着缓冲。尽管缓冲液的存在对光响应的上升阶段的影响可以忽略不计，但它深刻地改变了后来的行为。对短暂闪光的响应变得延长并表现出超调，显然是因为关闭过程被修改了。伴随更亮的闪光（光适应的早期迹象）而达到峰值的正常时间加速消失了。对稳定适应照明的响应需要比正常情况更长的时间才能达到稳定水平，尽管最终水平代表了类似的电流部分抑制。通过叠加测试闪光，这种适应照明的存在导致更快的恢复，而钙缓冲剂的存在减慢了恢复。结果与最近显示伴随光响应的Cai的快速下降参与终止光响应，并且Cai从而参与设置光转导的操作点和灵敏度的观点一致。通过与其他工作的比较，我们推断 Cai 似乎至少部分通过控制 cGMP 磷酸二酯酶活性来发挥作用。
Both cGMP and Ca2+ appear to be involved in the process of phototransduction in vertebrate rods, but their precise roles have been the subject of debate. To investigate the role of Ca2+ we have artificially increased the calcium buffering capacity of the rod by using a patch pipet to incorporate the calcium buffer 1,2-bis(o-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid (BAPTA) into the rod cytoplasm. In the presence of buffer the Na+-Ca2+ exchange current became greatly slowed, suggesting that the cytoplasmic calcium concentration (Cai) had indeed been buffered substantially. Although the presence of buffer had negligible effect on the rising phase of the light response, it profoundly altered the later behavior. Responses to brief flashes became prolonged and exhibited an overshoot, apparently because the shut-off process was modified. The normal acceleration of time-to-peak with brighter flashes (an early sign of light adaptation) disappeared. Responses to steady adapting illumination took much longer than normal to settle to a steady level, although the final level represented a similar fractional suppression of current. With superimposed test flashes the presence of such adapting illumination caused a more rapid recovery, whereas the presence of calcium buffer slowed the recovery. The results are consistent with the idea that the rapid drop in Cai, which has recently been shown to accompany the light response, is involved in terminating the light response, and that Cai is thereby involved in setting the operating point and sensitivity of phototransduction. From comparison with other work we infer that Cai appears to act, at least in part, by means of control of cGMP phosphodiesterase activity.