Investigation of factors that influence the temperature sensitivity of the TRPM2 cation channel.

Abstract

TRPM2 is a cation channel gated by Ca2+, ADPR and PiP2. The channel plays important role in the central and peripheral heat detection. To understand the physiological relevance of the channel in the regulation of body temperature we conducted electrophysiological studies in cell free patches at various temperatures and agonist concentrations. In the temperature range of 15-40°C we found that heating alone cannot open the channel, gating is strictly agonist dependent. Rising temperature increases channel conductance, open probability and apparent agonist binding affinities. We identified a strongly temperature dependent positive feedback on channel activity caused by the Ca2+ influx through the channel's pore. This temperature dependent Ca2+ influx generates a supraphysiological intracellular [Ca2+] nanodomain that tunes channel activity. These findings explain the physiological relevance of the channel in the regulation of body temperature. Based on our measured data we constructed a mechanistic gating model that allows the calculation of agonist concentrations in the channel's direct environment from measured open probabilities at given temperatures. This model allows us to further investigate the TRPM2 channel's temperature dependent function in different cellular environments and study how the resting membrane potential or the intracellular Ca2+ buffering properties modulate the channel's temperature threshold in different cell types.