Inositol 1,4,5-trisphosphate–induced Calcium Release Is Necessary for Generating the Entire Light Response of Limulus Ventral Photoreceptors

Abstract

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 μM 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.

Endoplasmic Reticulum Ca2+Handling in Excitable Cells in Health and Disease

“…For example, 2-APB was used to establish a role for IP 3 -induced Ca 2ϩ release in the generation of the entire physiological response of photoreceptors to light in the horseshoe crab (Fein, 2003); to show that IP 3 R are essential for the propagation of Ca 2ϩ oscillations in response to depolarization in sensory neurons (Zeng et al, 2008); and to demonstrate a pivotal role for IP 3 R-mediated Ca 2ϩ release in the vasoconstriction of small arteries (Snetkov et al, 2003). However, although 2-APB has been widely used to evaluate the involvement of IP 3 receptors in the generation of Ca 2ϩ signals, it is not a very specific agent.…”

Lipid signaling to membrane proteins: From second messengers to membrane domains and adapter-free endocytosis

“…Ironically, these seminal discoveries did not lead quickly to the identification of a second messenger that mediates invertebrate phototransduction. IP 3 appeared to be required for Limulus photo responses ( Brown et al, 1984 ), and it was later verified to be critical in Limulus in another JGP contribution ( Fein, 2003 ). However, IP 3 was eliminated as a possible second messenger in Drosophila , and interest turned to FFAs generated by DAG lipases subsequent to PIP 2 cleavage to DAG ( Chyb et al, 1999 ).…”

Calcium activates the light-dependent conductance in melanopsin-expressing photoreceptors of amphioxus

“…In invertebrates the gamut of proposed candidates includes IP 3 (31,32), Ca (33), DAG or metabolites thereof (34)(35)(36), PIP 2 (37), metabolic stress (38), capacitative Ca entry (39), protons (40), and mechanical forces (41). In fact, there are even indications that no universal mechanism may exists, because substances that exert a clear effect in one system, like PUFAs in Drosophila (35), proved inert in another, like Limulus (42), and vice versa (43). The situation is equally blurry for ipRGCs, where PUFAs and heparin proved ineffective, prompting the suggestion that neither downstream branch of the PLC cascade is involved; a possible role for PIP 2 was proposed instead (8).…”