Role Of Pip2 On Ca2+-Dependent Desensitization of Trpv2

Abstract

TRPV2 is a member of the transient receptor potential superfamily of ion channels involved in chemical and thermal pain transduction. Unlike the related TRPV1 channel, TRPV2 does not appear to bind either calmodulin or ATP in its N-terminal ankyrin repeat domain. In addition, it does not contain a calmodulin-binding site in the distal C-terminal region, as has been proposed for TRPV1. Importantly, though, we have found that TRPV2 undergoes Ca2+-dependent desensitization similar to TRPV1, suggesting that the mechanism of desensitization may be conserved in the two channels. To elucidate the molecular mechanism underlying Ca2+-dependent desensitization in TRPV2 we used whole-cell recordings of F-11 cells transiently transfected with TRPV2. We found that prolonged applications of the TRPV2 agonist 2-APB led to nearly complete desensitization of the channel in the presence of extracellular Ca2+. In contrast, no desensitization was observed in the absence of Ca2+. TRPV2 desensitization was not altered in whole-cell recordings in the presence of calmodulin inhibitors or upon co-expression of mutant calmodulin, suggesting that CaM does not play a major role in Ca2+-dependent desensitization of TRPV2. Interestingly, simultaneous confocal imaging and electrophysiological recording of whole cells expressing TRPV2 and a fluorescent PI(4,5)P2 binding probe showed a high degree of temporal correlation between the Ca2+ induced desensitization and depletion of PI(4,5)P2. Thus, Ca2+ influx through TRPV2 is sufficient to trigger a dramatic decrease in PI(4,5)P2 levels, presumably by activating PLC. We propose that the decrease in PI(4,5)P2 levels upon channel activation underlies at least a major component of Ca2+-dependent desensitization of TRPV2.