Excitation of
            <i>Limulus</i>
            Photoreceptors by Vanadate and by a Hydrolysis-Resistant Analog of Guanosine Triphosphate

Fein, Alan M.; Corson, D. Wesley

doi:10.1126/science.6782676

Cited by 63 publications

(31 citation statements)

References 13 publications

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“…After injection of this activator into the cell and stimulation of guanine nucleotide exchange by light there was a sustained increase in the frequency of discrete events in the dark, as previously reported for this and other G protein activators (17,31,32). Fig.…”

Section: Resultssupporting

confidence: 61%

Ca ²⁺ /calmodulin-binding peptides block phototransduction in Limulus ventral photoreceptors: Evidence for direct inhibition of phospholipase C

Richard

Ghosh²,

Lowenstein³

et al. 1997

Proc. Natl. Acad. Sci. U.S.A.

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Phototransduction in Limulus photoreceptors involves a G protein-mediated activation of phospholipase C (PLC) and subsequent steps involving InsP 3 -mediated release of intracellular Ca 2؉ . While exploring the role of calmodulin in this cascade, we found that intracellular injection of Ca 2؉ ͞calmodulin-binding peptides (CCBPs) strongly inhibited the light response. By chemically exciting the cascade at various stages, we found the primary target of this effect was not in late stages of the cascade but rather at the level of G protein and PLC. That PLC␦ 1 contains a calmodulin-like structure raised the possibility that PLC might be directly affected by CCBPs. To test this possibility, in vitro experiments were conducted on purified PLC. The activity of this enzyme was strongly inhibited by CCBPs and also inhibited by calmodulin itself. Our results suggest that the calmodulin-like region of PLC has an important role in regulating this enzyme.Phototransduction in Limulus photoreceptors is a complex excitation cascade that has sufficient amplification to produce large electrical events to single photons (1). The initial stage of this cascade resembles the rhodopsin͞G protein interaction found in vertebrate photoreceptors, but the enzyme activated by G protein is phosphoinositide-specific phospholipase C (PLC) rather than cGMP-phosphodiesterase. PLC, in turn, generates InsP 3 (2), and the resulting InsP 3 -mediated Ca 2ϩ release (3-5) leads to activation of nonspecific cation channels (2, 6), perhaps through an intermediate step involving cGMP (7,8).Invertebrate photoreceptors contain a high concentration of calmodulin (9). In the region of the photoreceptor specialized for phototransduction, the microvillar region, the concentration may be as high as 0.5 mM (10). Because the light-induced elevation of Ca 2ϩ plays an obligatory role in the excitation process in Limulus (11), we suspected that a calmodulindependent process might play an important role in a late stage of the excitation process, perhaps coupling the InsP 3 -mediated elevation of Ca 2ϩ to the opening of ion channels. If this were the case, calmodulin peptide antagonists should reduce the response to light. The experiments reported here show Ca 2ϩ ͞ calmodulin peptide antagonists do indeed have this effect. However our results show that the primary site of this effect is not at a late stage of transduction but rather an early stage involving PLC.PLC isoforms are found in all eukaryotic cells and are involved in signal transduction, including sensory, learningrelated synaptic plasticity, and oncogenesis (for reviews see refs. 12 and 13). Recently, the crystal structure of PLC␦ 1 has been obtained (14). This structure revealed EF-hand domains that resemble the structure of calmodulin with Ca 2ϩ bound (the ''calmodulin-like'' domain). Sequence alignment and ␣-helix prediction suggest the existence of similar structures in all PLC isozymes. The regulatory role of this region is unclear, but it seemed possible from our physiological results that it m...

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Section: Resultssupporting

confidence: 61%

Ca ²⁺ /calmodulin-binding peptides block phototransduction in Limulus ventral photoreceptors: Evidence for direct inhibition of phospholipase C

Richard

Ghosh²,

Lowenstein³

et al. 1997

Proc. Natl. Acad. Sci. U.S.A.

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“…7E). The variance of this noise was transiently reduced from 0.16 to 0.06 mV 2 after 20 msec flashes of light (log 10 Ϫ4.4) consistent with the adaptation of GTP-␥-Sinduced events (Fein and Corson, 1981). We therefore conclude that desensitization by (Ϫ)-indolactam V is downstream from rhodopsin.…”

Section: (؊)-Indolactam V Inhibits the Phototransduction Cascade At Tmentioning

confidence: 49%

Protein Kinase C Activators Inhibit the Visual Cascade inLimulusVentral Photoreceptors at an Early Stage

Dabdoub

Payne

1999

J. Neurosci.

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The phosphoinositide cascade mediates visual transduction in invertebrate photoreceptors. Phospholipase C (PLC) catalyzes the hydrolysis of phosphatidylinositol bisphosphate, producing inositol trisphosphate (InsP 3 ) and diacylglycerol (DAG). Protein kinase C (PKC) is a major target of DAG in many cell types. We have used PKC activators to investigate the function of the kinase in the phototransduction cascade in Limulus polyphemus ventral photoreceptors. Extracellular application of (Ϫ)-indolactam V (0.03-30 M) or phorbol-12,13-dibutyrate (10 M) reversibly reduced the sensitivity of the electrical response of the photoreceptors to light by up to 1000-fold. The inert stereoisomer (ϩ)-indolactam V and 4␣-phorbol had no effect. The effect of (Ϫ)-indolactam V was antagonized by the PKC inhibitors bisindolylmaleimide I and Gö 6976. Coapplication of bisindolylmaleimide V, used as a negative control compound for PKC inhibition, did not reduce the effectiveness of (Ϫ)-indolactam V. These findings are consistent with (Ϫ)-indolactam V activating PKC and desensitizing the light response. Furthermore, our pharmacological results indicate that PKC activation does not appear to play a role in light adaptation. We localized the position of the target of PKC in the visual cascade. We chemically excited the cascade at various stages to determine the kinase's target. PKC activation by (Ϫ)-indolactam V decreased the light-induced elevation of intracellular calcium but had no effect on the photoreceptor's excitatory response to intracellular injection of InsP 3 . However, the PKC activator greatly reduced the excitation caused by GTP-␥-S injection. We propose that PKC inhibits the visual transduction cascade at the G-protein and/or PLC stage.

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“…Furthermore, for invertebrate photoreceptors it has been shown that calcium flux is light dependent [16] and that calcium is an important agent in controlling membrane conductance [17] (see Stieve 1981). Pharmacological agents activating adenylate cyclase injected in Limulus photoreceptors induced depolarizations similar to light induced changes in membrane potentiaI (Fein and Corson 1981;see also Fein and Szuts 1982). Invertebrate rhodopsin can activate bovine PDE ) and a native GTPase (Calhoon et al 1980, Vandenberg andMontal 1982).…”

Section: Receptor Potentialmentioning

confidence: 91%

Progress in phototransduction

Stavenga

DeGrip

Grip

1983

Biophys. Struct. Mechanism

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Excitation of Limulus Photoreceptors by Vanadate and by a Hydrolysis-Resistant Analog of Guanosine Triphosphate

Cited by 63 publications

References 13 publications

Ca ²⁺ /calmodulin-binding peptides block phototransduction in Limulus ventral photoreceptors: Evidence for direct inhibition of phospholipase C

Ca ²⁺ /calmodulin-binding peptides block phototransduction in Limulus ventral photoreceptors: Evidence for direct inhibition of phospholipase C

Protein Kinase C Activators Inhibit the Visual Cascade inLimulusVentral Photoreceptors at an Early Stage

Progress in phototransduction

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Excitation of Limulus Photoreceptors by Vanadate and by a Hydrolysis-Resistant Analog of Guanosine Triphosphate

Cited by 63 publications

References 13 publications

Ca 2+ /calmodulin-binding peptides block phototransduction in Limulus ventral photoreceptors: Evidence for direct inhibition of phospholipase C

Ca 2+ /calmodulin-binding peptides block phototransduction in Limulus ventral photoreceptors: Evidence for direct inhibition of phospholipase C

Protein Kinase C Activators Inhibit the Visual Cascade inLimulusVentral Photoreceptors at an Early Stage

Progress in phototransduction

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Ca ²⁺ /calmodulin-binding peptides block phototransduction in Limulus ventral photoreceptors: Evidence for direct inhibition of phospholipase C

Ca ²⁺ /calmodulin-binding peptides block phototransduction in Limulus ventral photoreceptors: Evidence for direct inhibition of phospholipase C