Divalent heavy metal cations block the TRPV1 Ca(2+) channel

Area of Science:

• Ion Channel Physiology
• Neuropharmacology
• Toxicology

Background:

• Transient receptor potential vanilloid 1 (TRPV1) is a crucial non-selective cation channel.
• TRPV1 mediates pain sensation and is implicated in various physiological and pathological states.
• Understanding TRPV1 modulation by external factors like heavy metals is vital.

Purpose of the Study:

• To investigate the functional effects of selected heavy metal cations on TRPV1 channel activity.
• To determine the potency and mechanism of action of these cations as TRPV1 inhibitors.
• To assess the in vivo relevance of observed TRPV1 inhibition by heavy metals.

Main Methods:

• Electrophysiological assays to measure pore-blocking activity (IC50) of various cations (Co2+, Cd2+, Ni2+, Cu2+, Zn2+, Mg2+, Mn2+, La3+).
• Radioligand assays ((45)Ca2+ influx) to study cation interaction with TRPV1, including heat and vanilloid activation.
• Site-directed mutagenesis of the TRPV1 pore region and in vivo behavioral tests (nocifensive eye wipe response in mice).

Main Results:

• Cobalt (Co2+) emerged as the most potent TRPV1 blocker (IC50 = 13 μM), followed by Cd2+, Ni2+, and Cu2+.
• Zn2+ showed weak and partial inhibition, while Mg2+, Mn2+, and La3+ had minimal effects.
• Co2+ competed with and passed through the TRPV1 channel, accumulating in cells and neurons, and attenuated pain responses in vivo.

Conclusions:

• Divalent heavy metal cations, particularly Co2+, significantly inhibit TRPV1 channel function.
• Co2+ acts as a potent pore blocker and can traverse the TRPV1 channel, impacting pain signaling.
• Mutagenesis data suggest divalent cations share a common binding site involving negatively charged amino acids in the TRPV1 pore, similar to Ca2+.