The TRPM4 channel inhibitor 9-phenanthrol

Abstract

The phenanthrene-derivative 9-phenanthrol is a recently identified inhibitor of the transient receptor potential melastatin (TRPM) 4 channel, a Ca(2+) -activated non-selective cation channel whose mechanism of action remains to be determined. Subsequent studies performed on other ion channels confirm the specificity of the drug for TRPM4. In addition, 9-phenanthrol modulates a variety of physiological processes through TRPM4 current inhibition and thus exerts beneficial effects in several pathological conditions. 9-Phenanthrol modulates smooth muscle contraction in bladder and cerebral arteries, affects spontaneous activity in neurons and in the heart, and reduces lipopolysaccharide-induced cell death. Among promising potential applications, 9-phenanthrol exerts cardioprotective effects against ischaemia-reperfusion injuries and reduces ischaemic stroke injuries. In addition to reviewing the biophysical effects of 9-phenanthrol, here we present information about its appropriate use in physiological studies and possible clinical applications.

Keywords: 9-phenanthrol; NSCCa; TRPM4; calcium-activated non-selective cation channel; cardioprotection.

Figure 1

Chemical structures of pharmacological inhibitors of TRPM4 (9-phenanthrol, MPB-104, flufenamic acid, glibenclamide, quinine, quinidine) and NSC_Ca currents (DPC, DCDPC, NPPB). Under each compound, arrows indicate its other main targets among ion channels, in addition to TRPM4 and NSC_Ca currents. The list indicates typical targets, but is not exhaustive.

Figure 2

TRPM4 channel inhibition by 9-phenanthrol. Effect of 9-phenanthrol on TRPM4 currents after recombinant expression of the human TRPM4 gene in HEK-293 cells. (A) Concentration–response curve for the effects of 9-phenanthrol in the inside-out configuration (green squares) or whole-cell configuration (red circles). Fitting the Hill equation to the data points indicates a similar IC₅₀ at 2 × 10⁻⁵ mol·L⁻¹ and a Hill coefficient close to 1. The chemical structure of 9-phenanthrol is provided on the right. (B) Effect of 10⁻⁴ mol·L⁻¹ 9-phenanthrol applied to the inside of the membrane, on a representative current recording in the inside-out configuration (V_m = +40 mV). Around 80 channels were present in the patch. (C) Effect of 10⁻⁴ mol·L⁻¹ 9-phenanthrol applied to the outside of the membrane, on a representative whole-cell recording. The voltage command is a ramp from V_m = −100 to +100 mV. Note that the effects of 9-phenanthrol are reversible. See Grand et al. (2008) for protocol.

Figure 3

Effects of 9-phenanthrol on heart rhythm in a mouse isolated right atrium. Spontaneous action potentials were recorded using an intracellular microelectrode, while the right isolated atrium was superfused with oxygenated physiological solution. (A) Time course of the effect of 10⁻⁴ mol·L⁻¹ 9-phenanthrol on beating rate measured every 10 s as beats min^-1 (bpm). The application of 9-phenanthrol is indicated by the grey shading. Note that the effects of 9-phenanthrol were reversible. (B) Representative recordings for control, 9-phenanthrol, and washout, as indicated in (A) by arrows. See Hof et al. (2013) for protocols.

Figure 4

Cardioprotective effect of 9-phenanthrol. Anti-arrhythmic effects of 9-phenanthrol in a model of hypoxia-reoxygenation induced arrhythmias in mouse isolated ventricle. An isolated right ventricle was submitted to a hypoxic episode and then reoxygenated, which induces EADs. In this model, spontaneous beating was thought to arise from Purkinje fibres. (A) Time course of the effects of 10⁻⁴ mol·L⁻¹ 9-phenanthrol on the occurrence of EADs. The number of EADs was measured in successive 10 s windows. The application of 9-phenanthrol is indicated by the grey shading. Note the total and reversible abolition of arrhythmias after the application of 9-phenanthrol. (B) Representative recordings for control, 9-phenanthrol and washout. While several EADs were present in one-fifth of the action potentials in control, the rhythm was perfectly regular in the presence of 9-phenanthrol. See Simard et al. (2012a) for protocols.