Genetic evidence against involvement of TRPC proteins in SOCE, ROCE, and CRAC channel function

Abstract

Using genetically engineered mice andcell lines derived from genetically engineered mice we show that depletion ofER delimited Ca2+ stores activate heteromeric Ca2+ entry (SOCE)channels formed obligatorily, but not exclusively by Orai1 molecules.Comparison of Orai dependent Ca2+ entries revealed Orai1 to bedominant when compared to Orai2 and Orai3. Unexpectedly, we found that storedepletion activated Ca2+ entry does not depend obligatorily on functionallyintact TRPC molecules, as SOCE monitored with the Fura2 Ca2+reporter dye is unaffected in cells in which all seven TRPC coding genes havebeen structurally and functionally inactivated. Unexpectedly as well, we foundthat TRPC-independent Gq-coupled receptor operated Ca2+ entry (ROCE)also depends on Orai1. Biophysical measurements of Ca2+ releaseactivated Ca2+ currents (Icrac) are likewise unaffected by ablationof all seven TRPC genes. We refer to mice and cells carrying the seven-fold disruptionof TRPC genes as TRPC heptaKO mice and cells. TRPC heptaKO mice are fertile allowingthe creation of a new homozygous inbred strain.