Single‐channel properties of native and cloned rat vanilloid receptors

Abstract

The responses of single‐channel currents to capsaicin were recorded using the giga‐seal patch‐clamp technique in cell‐attached and excised (inside‐out/outside‐out) patches from embryonic rat dorsal root ganglion (DRG) neurones in culture and in Xenopus oocytes heterologously expressing the rat vanilloid receptor (rVR1). Native and cloned vanilloid receptor (VR)‐mediated currents exhibited outward rectification. In both the DRG neurones and oocytes expressing VR1, the chord conductances at −60 and +60 mV were ≈50 and ≈100 pS, respectively. At positive potentials, the channel exhibited a single conductance state. In contrast, at negative potentials, brief sojourns to subconductance states were apparent. The probability of the channel being open (Po) was dependent on the transmembrane voltage and the patch configuration (i.e. cell‐attached vs. excised). In both DRG neurones and oocytes, the Po was greater at positive (+60 mV) than at negative (‐60 mV) potentials. In cell‐attached patches, the Po was approximately twofold higher, regardless of the applied potential. Most likely, the outward rectification observed in whole‐cell currents is due to the voltage dependence of single‐channel conductance and Po. The open‐time distributions of single‐channel currents recorded from native and cloned VRs in the presence of low agonist concentrations (0.01‐0.03 μm) were best fitted with three exponential components. The closed‐time distributions were best fitted by five exponential components. At higher concentrations (0.5‐1 μm), an additional component was required to fit the open‐time distribution, and the number of exponential components needed to fit the closed‐time distributions was reduced to two. The overall mean open time at +60 mV was ≈4 ms, compared to ≈1.2 ms at −60 mV. However, the overall mean closed time was not voltage dependent. There were no significant differences between the native and cloned receptors. A comparison of single‐channel properties of native and heterologously expressed VR channels indicates that expression of the rVR1 subunit alone can account for the single‐channel behaviour of the majority of the native VRs. These results suggest that either native VRs are made up of VR1 subunits, or the incorporation of subunits other than VR1 does not influence the functional properties.

Cannabinoid WIN 55,212-2 Regulates TRPV1 Phosphorylation in Sensory Neurons

“…This difference may be due to the different sites of action of WIN and capsaicin. Capsaicin, acting on TRPV1, is known to induce a robust inward conductance of Ca 2ϩ ions with a current amplitude of ϳ6 -8 nA (by 10 M capsaicin) in sensory neurons (55), whereas WIN, acting on TRPA1, gates a much smaller inward current of ϳ250 pA (by 50 M WIN) in TG neurons. 5 The reduced current amplitude with WIN activation of TRPA1 in comparison with that with capsaicin activation of TRPV1 could partly explain the differences in the ability of each to desensitize I CAP .…”

Transient Receptor Potential Vanilloid 1 Involvement in Animal Pain Perception

“…Mice lacking the TRPV1 gene demonstrate deficits in thermal or inflammation pain, but maintain part of sensitivity to noxious heat (Premkumar et al, 2002). Moreover, TRPV1 deficient mice do not display thermal hypersensitivity following tissue injury (Caterina et al, 2000;Davis et al, 2000), substantiating the hypothesis that capsaicin receptor is a polymodal integrator of noxious chemical and physical stimuli in vivo (Jordt and Julius, 2002;Rehman et al, 2013).…”

“…TRPV1 is a non-selective cation channel that has a high permeability to Ca 2+ and its activation induces sensory nerve endings depolarization and evokes a series of responses that propagates from the spinal cord to the brain (Premkumar et al, 2002;De Petrocellis and Moriello, 2013). It contributes to the detection of noxious thermal stimuli by primary sensory neurons of the pain pathway (Tominaga et al, 1998;Caterina and Julius, 2001).…”

The Mystery of P2X7 Ionotropic Receptor: From a Small Conductance Channel to a Large Conductance Channel

“…The single-channel amplitude at +60 mV was 5.3 pA, corresponding to a conductance of 88.3 pS. Open probability depends on membrane potential as it has been shown in single-channel and whole-cell recordings (Premkumar et al 2002;Voets et al 2004b). At the molecular level, an extracellular Ca 2+ -dependent reduction of TRPV1 responsiveness upon continuous vanilloid exposure (electrophysiological desensitization) may underlie this phenomenon, at least in part (Caterina et al, 1997;Szallasi & Blumberg, 1999).…”