QX 222

Coapplication of lidocaine and membrane-impermeable lidocaine derivative QX-222 produces divergent effects on evoked and spontaneous nociceptive behaviors in mice.[Pubmed:25506595]

Biomed Res Int. 2014;2014:628729.

The present study was aimed at investigating the analgesic properties of a combination of lidocaine and QX-222 and its effects on evoked pain behavior (complete Freund's adjuvant-induced allodynia and hyperalgesia in inflammatory condition) and spontaneous pain behavior (formalin-induced acute pain) in mice. Drugs were injected adjacent to sciatic nerve or into plantar. Motor function, thermal withdrawal latency, mechanical withdrawal threshold, and licking/biting were evaluated by behavioral tests. A combination of lidocaine and QX-222 adjacent sciatic nerve injection produced the long-lasting sensory-specific nerve block, and intraplantar injection inhibited spontaneous pain in the formalin-treated mice but did not detectably attenuated hyperalgesia and allodynia in the complete Freund's adjuvant- (CFA-) treated mice. Our results suggest that a combination of lidocaine and QX-222 achieves a long-lasting differential block (sensory selective) and produces divergent effects on evoked and spontaneous pain behaviors in mice.

Cooperative interactions between general anesthetics and QX-222 within the pore of the acetylcholine receptor ion channel.[Pubmed:7520126]

Mol Pharmacol. 1994 Jul;46(1):169-75.

To test the hypothesis that general anesthetics block nicotinic acetylcholine receptor channels by binding within the pore of the channel, we looked for competitive interactions between ether and QX-222 at the single channel current level. Experiments were performed on outside-out patches excised from BC3H-1 cells. QX-222 causes channels to flicker as it repeatedly binds within the pore of the channel and blocks the flow of current through the channel. Ether reduces the apparent unitary conductance of the channel. This effect of ether may be due to frequent, short-lived, unresolved, blockages of the channel. When both ether and QX-222 are applied, the effects of both drugs are seen on single channels. However, the duration of QX-222 blocking events are longer when ether is present; the duration of block is 0.89 +/- 0.06 ms with 30 microM QX-222 alone and 2.23 +/- 0.37 ms with 30 microM QX-222 + 20 mM ether (n = 5 +/- S.D.; -100 mV). Similar results are obtained when butanol is used in place of ether. We conclude that ether and QX-222 do not compete for a common binding site. Conversely, ether decreases the dissociation rate of QX-222. The simplest interpretation of these data is that the binding sites for ether and the aromatic moiety of QX-222 are distinct but close to each other; when ether is bound to its site, the binding of QX-222 is stabilized. We cannot, however, discount the possibility that ether stabilizes QX-222 by binding to a remote site and allosterically modifying the pore of the channel.

The voltage dependence of recovery from use-dependent block by QX-222 separates mechanisms for drug egress in the cardiac sodium channel.[Pubmed:16637111]

Biochem Pharmacol. 2006 Apr 28;71(9):1299-1307.

In neuronal sodium channels of squid giant axons, recovery from QX-222 block is slowed by hyperpolarization. However, in ventricular cells, hyperpolarization speeds recovery. Previously, we showed that isoform-specific residues in the external side of the cardiac sodium channel isoform (D1P-loop C373 and D4S6 T1752) influence use-dependent block (UDB) by lidocaine. To determine whether these isoformspecific residues contribute to the contrasting voltage-dependent recovery observed in ventricular myocytes, we measured recovery rates from UDB by QX-222 at holding potentials of 120, 140, 160 and 180 mV for wild-type cardiac channel (WT), the mutants C373Y (CY) and T1752V (TV), and C373Y/T1752V (CY/TV). Unlike neuronal channels, cardiac sodium channels recovered from QX block faster at hyperpolarized potentials. All mutations slowed QX-222 recovery, with the greatest rate reduction observed for the double mutant, indicating that the isoform-specific residues define external drug paths. The recovery rates varied linearly with voltage over the range tested, and we used the slopes of rate versus voltage plots to quantify voltage dependence. The TV mutation caused reduction in recovery rates without changing the slope, indicating that the mutation closed a voltage-independent egress path. The CY mutation, however, flattened the slope and reduced the voltage dependence of recovery. In addition, the reduction in rate caused by CY/TV is less than the sum of those for CY and TV, suggesting that the impacts of these two residues are interrelated. Therefore, we propose that the isoform-specific residues C373 and T1752 change recovery from UDB by distinct mechanisms but determine a common drug egress path.

Blockade of lysophosphatidylcholine-modified cardiac Na channels by a lidocaine derivative QX-222.[Pubmed:8770124]

Am J Physiol. 1996 Aug;271(2 Pt 2):H790-7.

Single Na channels from rat and rabbit ventricular cells were studied with use of the excised inside-out patch-clamp technique. To investigate local anesthetic interactions with Na channels modified by the ischemic metabolite lysophosphatidylcholine (LPC), the quaternary ammonium lidocaine derivative QX-222 [2-(trimethylamino)-N-(2,6-dimethylphenyl)acetamide] was applied to the cytoplasmic side of patches from untreated cells and from those treated with LPC for approximately 1 h. Single-channel amplitudes and kinetics for unmodified channels were similar to those reported previously for cardiac cells with a single-component, mean-channel open time. LPC-modified channels showed prolonged open channel bursting with a two-component, mean open time, suggesting two open states. Conductance sublevels to the 60-70% level of the main conductance were found in both unmodified and LPC-modified channels and also with and without QX-222 present. QX-222 reversibly shortened the open time of the unmodified channel and for both open times of the LPC-modified channel without decreasing single-channel amplitude. Calculated association rates for QX-222 with the channel were found to be greater for the open states of the modified channel than those for the unmodified channel. Thus the lidocaine analogue QX-222 interacts with and blocks the open state of both unmodified and LPC-modified, cardiac Na channels. The blocking effect on LPC-modified channels would be predicted to be greater both because of the longer dwell time in the high-affinity open states for modified channels and also because of an intrinsically greater association rate in the modified channels.

Local anaesthetic blockade of neuronal nicotinic ACh receptor-channels in rat parasympathetic ganglion cells.[Pubmed:7517326]

Br J Pharmacol. 1994 Mar;111(3):663-72.

1 The effects of the local anaesthetics QX-222 and procaine on nicotinic acetylcholine (ACh)-evoked currents in cultured parasympathetic cardiac neurones of the rat were investigated by use of the whole-cell, perforated-patch, and outside-out recording configurations of the patch clamp method. 2 QX-222 and procaine, applied to the extracellular surface, reversibly inhibited the peak amplitude of the whole-cell nicotinic ACh-evoked current in a concentration-dependent manner, with half-maximal inhibitory concentrations (IC50) of 28 microM and 2.8 microM, respectively, at -80 mV. In these neurones, the sustained inward current mediated by M1 muscarinic receptor activation was unaltered by QX-222, and neither local anaesthetic affected the adenosine 5'-triphosphate (ATP)-evoked current. 3 QX-222 and procaine block of nicotinic ACh-evoked inward current was voltage-dependent and enhanced by hyperpolarization. An e-fold change in their dissociation equilibrium constants (Kd) resulted from a 62 mV and a 122 mV change in membrane potential, respectively. 4 Both local anaesthetics produce a concentration-dependent increase in the half-time of decay of the nicotinic ACh-evoked inward current. 5 Measurements of unitary currents in outside-out patches showed that QX-222 reversibly increased the mean burst duration and closed time and reduced the mean channel open time and open-state probability of the nicotinic ACh receptor-channel (AChR) in a concentration-dependent manner. 6 The Kd and voltage sensitivity of local anaesthetic block of the nicotinic AChR in rat intracardiac neurones suggests that the pore-forming region of this channel differs from that of the AChR in frog and rat skeletal muscle and from the neuronal alpha 4 beta 2 ACh receptor-channel.