Acta Pharmacologica Sinica 2008 January; 29 (1): 90-97; doi: 10.1111/j.1745-7254.2008.00721.x

Aim: 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 µmol/L carbachol to, or dialysis of the cell with 100 µmol/L guanosine 5'-3-O-(thio)triphosphate (GTPγS), 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, N',N'-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 µmol/L) did not undergo the inhibition persisting after Ca²⁺ removal. Interestingly, the inclusion of inositol 1,4,5 trisphosphate (IP₃; 100 µmol/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.

Conclusion: 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.

Keywords: canonical transient receptor potential 7; calcium; inactivation, diacylglycerol; inositol 1,4,5 trisphosphate