Synergistic actions of diacylglycerol and inositol 1,4,5 trisphosphate for Ca2+-dependent inactivation of TRPC7 channel.
OBJECTIVE
The aim of the present study was to explore the mechanism for the Ca2+- dependent inactivation of the canonical transient receptor potential (TRPC) 7 channel expressed in human embryonic kidney 293 cells.


METHODS
The whole-cell patch-clamp technique was used in the study.


RESULTS
With Ca2+-free external solution, the perfusion of 100 micromol/L carbachol to, or dialysis of the cell with 100 micromol/L guanosine 5'-3-O-(thio)triphosphate (GTPgammaS), induced large inward currents, respectively. These currents were rapidly inhibited by the addition of 1 mmol/L Ca2+ into the bath, and recovery from this inhibition was only partial after the Ca2+ removal, unless vigorous intracellular Ca2+ buffering with 10 mmol/L 1,2 bis(2- aminophenoxy)ethane-N,N,No,No-tetraacetic acid (BAPTA) (plus 4 mmol/L Ca2+) was employed. In contrast, the current induced by a membrane-permeable analog of diacylglycerol (DAG), 1-oleoyl-2-acetyl-sn-glycerol (OAG; 100 micromol/L) did not undergo the inhibition persisting after Ca2+ removal. Interestingly, the inclusion of inositol 1,4,5 trisphosphate (IP3; 100 micromol/L) in the patch pipette rendered the OAG-induced current susceptible to the persistent Ca2+-mediated inhibition independent of the IP3 receptor in the majority of the tested cells, as evidenced by the inability of heparin and thapsigargin in reversing the effect of IP3.


CONCLUSIONS
The present results suggest that Ca2+ entry via the activated TRPC7 channel plays a critical role in inactivating the channel where the cooperative actions of DAG and IP3 are essentially involved.
Zhang
Hua
H
Department of Anatomy and KK Leung Brain Research Centre, The Fourth Military Medical University, Xi'an, China.
Inoue
Ryuji
R
Shi
Juan
J
Jin
Xiao-hang
XH
Li
Yun-qing
YQ
D002118:Calcium / Q000378:metabolism / Q000502:physiology*; D002460:Cell Line; D004075:Diglycerides / Q000494:pharmacology*; D004357:Drug Synergism; D004594:Electrophysiology; D016244:Guanosine 5'-O-(3-Thiotriphosphate) / Q000494:pharmacology; D006801:Humans; D007293:Inosine Triphosphate / Q000494:pharmacology*; D018408:Patch-Clamp Techniques; D050052:TRPC Cation Channels / Q000037:antagonists & inhibitors*
D004075:Diglycerides; D050052:TRPC Cation Channels; C498501:TRPC7 protein, human; D007293:Inosine Triphosphate; D016244:Guanosine 5'-O-(3-Thiotriphosphate); C038237:1-oleoyl-2-acetylglycerol; D002118:Calcium