Rat descending vasa recta express a tetrodotoxin (TTX) sensitive voltage-operated Na⁺ (Na_V) conductance. We examined expression of Na_V isoforms in DVR and tested for regulation of Na_V currents by calmodulin (CaM). RT-PCR in isolated permeabilized DVR using degenerate primers targeted to TTX sensitive isoforms amplified a product whose sequence identified only Na_V1.3. Immunoblot of outer medullary homogenate verified Na_V expression and fluorescent immunochemistry showed Na_V expression in isolated vessels. Immunochemistry in outer medullary serial sections confirmed that Na_V1.3 is confined to -smooth muscle actin positive vascular bundles. Na_V1.3 possesses a C-terminal CaM binding motifs. Using pull down assays and immunoprecipitation experiments we verified that CaM binds to either full length Na_V1.3 or a GST-Na_V1.3 C-terminal fusion protein. In patch clamp experiments, Na_V currents were suppressed by calmodulin inhibitory peptide (CIP, 100 nM) or the CaM inhibitor, N-(6-aminohexyl)-5-chloro-1-naphthalene-sulphonamide hydrochloride (W7). Neither CIP nor W7 altered the voltage dependence of pericyte Na_V currents, however raising electrode free Ca2+ from 20 to ~2000 nM produced a depolarizing shift of activation. In vitro, binding of CaM to GST-Na_V1.3C was not affected by Ca2+ concentration. We conclude that Na_V1.3 is expressed by DVR, binds to CaM and is regulated by CaM and Ca²⁺. Inhibition of CaM binding suppresses pericyte Na_V currents.