Cornwall M C, Matthews H R, Crouch R K, Fain G L
Department of Physiology, Boston University School of Medicine, Massachusetts 02118, USA.
J Gen Physiol. 1995 Sep;106(3):543-57. doi: 10.1085/jgp.106.3.543.
We have used suction electrode recording together with rapid steps into 0.5 mM IBMX solution to investigate changes in guanylyl cyclase velocity produced by pigment bleaching in isolated cones of the salamander Ambystoma tigrinum. Both backgrounds and bleaches accelerate the time course of current increase during steps into IBMX. We interpret this as evidence that the velocity of the guanylyl cyclase is increased in background light or after bleaching. Our results indicate that cyclase velocity increases nearly linearly with increasing percent pigment bleached but nonlinearly (and may saturate) with increasing back-ground intensity. In cones (as previously demonstrated for rods), light-activated pigment and bleached pigment appear to have somewhat different effects on the transduction cascade. The effect of bleaching on cyclase rate is maintained for at least 15-20 min after the light is removed, much longer than is required after a bleach for circulating current and sensitivity to stabilize in an isolated cone. The effect on the cyclase rate can be completely reversed by treatment with liposomes containing 11-cis retinal. The effects of bleaching can also be partially reversed by beta-ionone, an analogue of the chromophore 11-cis-retinal which does not form a covalent attachment to opsin. Perfusion of a bleached cone with beta-ionone produces a rapid increase in circulating current and sensitivity, which rapidly reverses when the beta-ionone is removed. Perfusion with beta-ionone also causes a partial reversal of the bleach-induced acceleration of cyclase velocity. We conclude that bleaching produces an "equivalent background" excitation of the transduction cascade in cones, perhaps by a mechanism similar to that in rods.
我们使用吸力电极记录，并结合快速切换到0.5 mM异丁基-甲基黄嘌呤（IBMX）溶液的方法，来研究在虎纹钝口螈分离视锥细胞中色素漂白所产生的鸟苷酸环化酶活性变化。在切换到IBMX溶液的过程中，背景光和漂白处理均加速了电流增加的时间进程。我们将此解释为鸟苷酸环化酶活性在背景光下或漂白后增加的证据。我们的结果表明，环化酶活性随色素漂白百分比的增加几乎呈线性增加，但随背景强度的增加呈非线性增加（且可能达到饱和）。在视锥细胞中（如之前在视杆细胞中所证明的），光激活色素和漂白色素对视转导级联反应似乎有 somewhat 不同的影响。在光照去除后，漂白对环化酶速率的影响至少维持15 - 20分钟，这比对分离视锥细胞中循环电流和敏感度在漂白后达到稳定所需的时间长得多。用含有11 - 顺式视黄醛的脂质体处理可完全逆转对环化酶速率的影响。β - 紫罗兰酮（一种发色团11 - 顺式视黄醛的类似物，它不与视蛋白形成共价连接）也可部分逆转漂白的影响。用β - 紫罗兰酮灌注漂白的视锥细胞会使循环电流和敏感度迅速增加，当去除β - 紫罗兰酮时，这种增加会迅速逆转。用β - 紫罗兰酮灌注还会导致漂白诱导的环化酶活性加速的部分逆转。我们得出结论，漂白可能通过与视杆细胞中类似的机制，对视锥细胞中的转导级联反应产生“等效背景”激发。
