Further Evidence of an Alternative Ion Permeation Pathway in the Nociceptor TRPM3

Abstract

TRPM3 is a member of the melastatin family of the transient receptor potential (TRP) channels and was described as a nociceptor. It can be activated by a multitude of stimuli, including chemical compounds such as pregnenolone sulphate (PS) or nifedipine (Nif), as well as by physical signals like temperature. Activation of TRPM3 by all these different type of stimuli leads to the opening of a central pore that is formed by the transmembrane domains five (S5) and six (S6) and the interconnecting pore-loop, resulting in an outward rectifying current-voltage relationship. Recently, we have described the existence of an alternative ion permeation pathway in TRPM3. This alternative pathway could be opened by simultaneous application of PS and the antifungal drug clotrimazole (Clt), resulting in a current shape that showed an in- and outward rectification. Very recently, we have described a novel synthetic agonist of TRPM3, CIM0216, which is remarkable by the fact that it is able to open as single compound both, the central pore and the alternative ion permeation pathway.By the use of CIM0216, we were able to further investigate the biophysical properties of the alternative ion permeation pathway and to achieve further evidence of the existence of an alternative ion permeation pathway in TRPM3. In addition, new mutagenesis studies of TRPM3 provided further evidence for the location of the alternative ion permeation pathway within the region of S4 of the voltage sensing domain.All together, these data provide more evidence for the existence of an alternative ion permeation pathway in TRPM3 that will open upon displacement of the voltage sensing domain S4.