We have compared activation by heat of TRPV4 channels, heterogeneously expressed in HEK293 cells, and endogenous channels in mouse aorta endothelium (MAEC). Increasing the temperature above 25 degrees C activated currents and increased [Ca(2+)](i) in HEK293 cells transfected with TRPV4 and in MAEC. When compared with activation of TRPV4 currents by the selective ligand 4alphaPDD (alpha-phorbol 12,13-didecanoate), heat-activated currents in both systems showed the typical biophysical properties of currents through TRPV4, including their single channel conductance. Deletion of the three N-terminal ankyrin binding domains of TRPV4 abolished current activation cells by heat in HEK293. In inside-out patches, TRPV4 could not be activated by heat but still responded to the ligand 4alphaPDD. In MAEC, the same channel is activated under identical conditions as in the HEK expression system. Our data indicate that TRPV4 is a functional temperature-sensing channel in native endothelium, that is likely involved in temperature-dependent Ca(2+) signaling. The failure to activate TRPV4 channels by heat in inside-out patches, which responded to 4alphaPDD, may indicate that heat activation depends on the presence of an endogenous ligand, which is missing in inside-out patches.