Synergistic actions of diacylglycerol and inositol 1,4,5 trisphosphate for Ca2+-dependent inactivation of TRPC7 channel1

Authors


  • 1

    This work was supported by the National Natural Science Foundation of China (No 30400154 and 30400329), Innovation Research Team Program of Ministry of Education (No IRT0560), and the National Program of Basic Research of China (No G2006CB500808).

Correspondence to Dr Juan SHI. Phn 86-29-8477-3074 Fax 86-29-8328-3229. E-mail shixjuan@yahoo.com

Abstract

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. Method: 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.

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