Fluorophore-assisted Light Inactivation Produces Both Targeted and Collateral Effects on N-type Calcium Channel Modulation in Rat Sympathetic Neurons.
From: Laboratory of Molecular Physiology, National Institute on Alcohol Abuse and Alcoholism, 5625 Fishers Lane, Room TS-06, MSC 9411, Bethesda, MD, 20892-9941 USA.
The Journal of physiology
- Publish Date: Oct 2006
- ISSN: 0022-3751
- Volume: 576
- Issue: Pt 2
- Pages: 477-92
- Medium: Print
- Language: English
- Citation (JAMA): Guo Juan, Chen Huanmian, Puhl Henry L, et al. Fluorophore-assisted Light Inactivation Produces Both Targeted and Collateral Effects on N-type Calcium Channel Modulation in Rat Sympathetic Neurons.. J. Physiol. (Lond.) Oct 2006;576:477-92
Abstract
Fluorophore-assisted light inactivation (FALI) is a method to inactivate specific proteins on a time scale of seconds to minutes using either diffuse or coherent light. Here we examine a novel FALI modality that utilizes a fluorescein-conjugated polypeptide, alpha-bungarotoxin (BTX) and a 13 amino acid BTX-binding site engineered into the N-terminus of metabotropic glutamate receptor 8a (mGluR8a), a class C G-protein-coupled receptor (GPCR). The tagged mGluR8a was expressed in rat sympathetic neurons and labelled with fluorescein-conjugated BTX (FL-BTX). The efficacy of FALI was evaluated by monitoring mGluR8a-mediated inhibition of calcium currents (I(Ca)) using whole-cell voltage-clamp techniques. Following either wide-field or laser illumination of FL-BTX-labelled neurons, mGluR8a-mediated I(Ca) inhibition was greatly attenuated whereas holding current and basal I(Ca), measures of non-specific effects, were minimally affected. Sodium azide, a collision quencher of singlet oxygen, reduced the magnitude of FALI-mediated effects supporting a role for reactive oxygen species in the process. Although these results were consistent with an acute inactivation of mGluR8a, the intended target, two findings confounded this interpretation. First, effects on a natively expressed signalling pathway, alpha(2)-adrenergic receptor-mediated I(Ca) modulation, were observed following illumination of neurons expressing FL-BTX-labelled sodium channel beta2 subunits or ionotropic 5-HT(3) receptors, proteins with no overt relationship to GPCR signalling pathways. Second, GPCR-independent I(Ca) modulation induced with intracellular guanylyl imidophosphate was also attenuated by FALI. These data challenge the assumption that the fluorophore-tagged protein is the sole target of FALI and provide evidence that collateral damage to proximal proteins occurs following fluorophore illumination.
Mesh Headings (Keywords): Animals, Binding Sites, Bungarotoxins, Calcium Channels, N-Type, Cell Line, Fluorescein, Fluorescent Dyes, Humans, Light, Male, Neurons, Patch-Clamp Techniques, Rats, Rats, Wistar, Receptors, G-Protein-Coupled, Receptors, Metabotropic Glutamate, Signal Transduction, Sympathetic Nervous System, Time Factors
Check for Full Text / PubMed Unique Identifier (PMID): 16873413
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