Fein Alan
Department of Physiology, University of Connecticut Health Center, Farmington, CT 06030-3505, USA.
J Gen Physiol. 2003 May;121(5):441-9. doi: 10.1085/jgp.200208778.
The experiments reported here were designed to answer the question of whether inositol 1,4,5-trisphosphate (IP3)-induced calcium release is necessary for generating the entire light response of Limulus ventral photoreceptors. For this purpose the membrane-permeable IP3 receptor antagonist 2-aminoethoxydiphenyl borate (2APB) (Maruyama, T., T. Kanaji, S. Nakade, T. Kanno, and K. Mikoshiba. 1997. J. Biochem. (Tokyo). 122:498-505) was used. Previously, 2APB was found to inhibit the light activated current of Limulus ventral photoreceptors and reversibly inhibit both light and IP3 induced calcium release as well as the current activated by pressure injection of calcium into the light sensitive lobe of the photoreceptor (Wang, Y., M. Deshpande, and R. Payne. 2002. Cell Calcium. 32:209). In this study 2APB was found to inhibit the response to a flash of light at all light intensities and to inhibit the entire light response to a step of light, that is, both the initial transient and the steady-state components of the response to a step of light were inhibited. The light response in cells injected with the calcium buffer 1,2-bis(o-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid (BAPTA) was reversibly inhibited by 2APB, indicating that these light responses result from IP3-mediated calcium release giving rise to an increase in Cai. The light response obtained from cells after treatment with 100 microM cyclopiazonic acid (CPA), which acts to empty intracellular calcium stores, was reversibly inhibited by 2APB, indicating that the light response after CPA treatment results from IP3-mediated calcium release and a consequent rise in Cai. Together these findings imply that IP3-induced calcium release is necessary for generating the entire light response of Limulus ventral photoreceptors.
对于鲎腹侧光感受器产生整个光反应而言，肌醇1,4,5 -三磷酸（IP3）诱导的钙释放是否必要。为此，使用了膜通透性IP3受体拮抗剂2 -氨基乙氧基二苯硼酸盐（2APB）（丸山，T.，T. 金治，S. 中出，T. 菅野，和K. 三木志保。1997. 《生物化学杂志》（东京）。122:498 - 505）。此前发现，2APB可抑制鲎腹侧光感受器的光激活电流，并可逆地抑制光和IP3诱导的钙释放以及通过向光感受器的光敏叶压力注射钙所激活的电流（王，Y.，M. 德什潘德，和R. 佩恩。2002. 《细胞钙》。32:209）。在本研究中，发现2APB在所有光强度下均抑制对闪光的反应，并抑制对光阶跃的整个光反应，也就是说，对光阶跃反应的初始瞬态和稳态成分均被抑制。注射钙缓冲剂1,2 -双（邻氨基苯氧基）乙烷 - N,N,N',N' - 四乙酸（BAPTA）的细胞中的光反应被2APB可逆地抑制，这表明这些光反应是由IP3介导的钙释放导致胞内钙（Cai）增加所引起的。用100微摩尔/升环匹阿尼酸（CPA）处理细胞以耗尽细胞内钙库后获得的光反应被2APB可逆地抑制，这表明CPA处理后的光反应是由IP3介导的钙释放以及随之而来的Cai升高所导致的。这些发现共同表明，IP3诱导的钙释放对于鲎腹侧光感受器产生整个光反应是必要的。
