Obligatory Participation of TRPC3 and/or TRPC6 in Cardiac Muscle Store Operated Ca2+ Entry (SOCE). Pharmacologic and Genetic Evidence

KARINA FORMOSO; SEBASTIÁN SUSPERREGUY; HE, XIJU; LIU, BENJU; LUTZ BIRNBAUMER

Simposio; 42nd Symposium on Hormones and Cell Regulation (ESE); 2017

Electrophysiological data indicate that storeoperated Ca entry channels are heterogeneous. CRAC channels are formed of Orai1are inwardly rectifying and Ca selective, SOC channels are TRPC1-based,minimally rectifying and rather non-selective. Neither type of channels are universally functionally expressed.  Cells exist (i.e. HEK-293) from which it isalmost impossible to record either CRAC currents or SOC currents. Yet in allcells store depletion (eg by Thapsigargin [Tg]) generates robust Store OperatedCa2+ Entry (SOCE) when monitored with FURA2, highlighting a void our knowledge of themolecular makeup of SOCE channels.  Here we report that  Tg-evoked SOCE in neonatal cardiomyocytes andH9c2 cardiomyoblasts is inhibited by about 80% by 5 uM of thepanTRPC inhibitor SKF96365 (SKF), aconcentration that does not inhibit Orai1-based SOCE as evoked in Orai1 plusSTIM1 transfected HEK293 cells. On the other hand,the Orai1 inhibitor AnCoA4, only partially inhibited Tg-evoked SOCE in neonatalcardiomyovytes and H9c2 cardiomyoblasts. This suggests participation of TRPCs in cardiomyocyte SOCE. SOCEin neonatal cardiomyocytes from Trpc3/6/7 triple knockout  mice was reduced by60% confirming the role of TRPCs in cardiac SOCE. Cardiomyocytes express TRPC1,TRPC2, TRPC3, TRPC4 and TRPC6, but not TRPC5 or TRPC7. In aggregate, the dataagree with a model in which  in additionto TRPC 3 an 6 (absent in the TKO), TRPC1, 2 and 4  may also contribute to the make up ofcardiomyocyte SOCE channels. These TRPCs would  be responsible for about 20% of SOCE.The 20% SOCE not inhibited by SKF is likely to be Orai1-based as suggested by the AnCoA4 inhibition data.