TRP4 (CCE1) protein is part of native calcium release-activated Ca2+-like channels in adrenal cells

Mammalian TRP proteins have been implicated to function as ion channel subu nits responsible for agonist-induced Ca2+ entry. To date, TRP proteins have been extensively studied by heterologous expression giving rise to diverse channel properties and activation mechanisms including store-operated mech anisms. However, the molecular structure and the functional properties of n ative TRP channels still remain elusive. Here we analyze the properties of TRP4 (CCE1) channels in their native environment and characterize TRP expre ssion patterns and store-operated calcium currents that are endogenous to b ovine adrenal cells. We show by Northern blot analysis, immunoblots, and im munohistochemistry that TRP4 transcripts and TRP4 protein are present in th e adrenal cortex but absent in the medulla, Correspondingly, bovine adrenal cortex cells express TRP4 abundantly. The only other TRP transcript found at considerable levels was TRP1, whereas TRP2, TRP3, TRP5(CCE2), and TRP6 w ere not detectable. Depletion of calcium stores with inositol 1,4,5-trispho sphate or thapsigargin activates store operated ion channels in adrenal cel ls. These channels closely resemble calcium release-activated Ca2+ (CRAC) c hannels. Expression of trp4(CCE1) cDNA in antisense orientation significant ly reduces both, the endogenous CRAC-like currents and the amount of native TRP4 protein. These results demonstrate that TRP4 contributes essentially to the formation of native CRAC-like channels in adrenal cells.