Human podocytes express functional thermosensitive TRPV channels

Heat-sensitive transient receptor potential vanilloid (TRPV) channels are expressed in various epithelial tissues regulating, among else, barrier functions. Their expression is well established in the distal nephron; however, we have no data about their presence in podocytes. As podocytes are indispensable in the formation of the glomerular filtration barrier, we investigated the presence and function of Ca²⁺ -permeable TRPV1-4 channels in human podocyte cultures.

Expression of TRPV1-4 channels was investigated at protein (immunocytochemistry, Western blot) and mRNA (Q-PCR) level in a conditionally immortalized human podocyte cell line. Channel function was assessed by measuring intracellular Ca²⁺ concentration using Flou-4 Ca²⁺ -indicator dye and patch clamp electrophysiology upon applying various activators and inhibitors.

Thermosensitive TRP channels were expressed in podocytes. The TRPV1-specific agonists capsaicin and resiniferatoxin did not affect the intracellular Ca²⁺ concentration. Cannabidiol, an activator of TRPV2 and TRPV4 channels, induced moderate Ca²⁺ -influxes, inhibited by both tranilast and HC067047, blockers of TRPV2 and TRPV4 channels respectively. The TRPV4-specific agonists GSK1016790A and 4α-phorbol 12,13-didecanoate induced robust Ca²⁺ -signals which were abolished by HC067047. Non-specific agonists of TRPV3 channels induced marked Ca²⁺ transients. However, TRPV3 channel blockers, ruthenium red and isopentenyl diphosphate only partly inhibited the responses and TRPV3 silencing was ineffective suggesting remarkable off-target effects of the compounds.

Our results indicate the functional presence of TRPV4 and other thermosensitive TRPV channels in human podocytes and raise the possibility of their involvement in the regulation of glomerular filtration barrier.