Properties of heterologously expressed hTRP3 channels in bovine pulmonary artery endothelial cells

1. We combined patch clamp and fura-2 fluorescence methods to characterize human TRP3 (hTRP3) channels heterologously expressed in cultured bovine pulmonary artery endothelial (CPAE) cells, which do not express the bovine trp3 isoform (btrp3) but express btrp1 and btrp4. 2. ATP, bradykinin and intracellular InsP₃ activated a non-selective cation current (I(hTRP3)) in htrp3-transfected CPAE cells but not in non-transfected wild-type cells. During agonist stimulation, the sustained rise in [Ca²⁺](i) was significantly higher in htrp3-transfected cells than in control CPAE cells. 3. The permeability for monovalent cations was P(Na) > P(Cs) ≃ P(K) >> P(NMDG) and the ratio P(Ca)/P(Na) was 1.62 ± 0.27 ( n = 11). Removal of extracellular Ca²⁺ enhanced the amplitude of the agonist-activated I(hTRP3) as well as that of the basal current The trivalent cations La³⁺ and Gd³⁺ were potent blockers of I(hTRP3) (the IC₅₀ for La³⁺ was 24.4 ± 0.7 μM). 4. The single-channel conductance of the channels activated by ATP, assessed by noise analysis, was 23 pS. 5. Thapsigargin and 2,5-di-tert-butyl-1,4-benzohydroquinone (BHQ), inhibitors of the organellar Ca²⁺-ATPase, failed to activate I(hTRP3). U-73122, a phospholipase C blocker, inhibited I(hTRP3) that had been activated by ATP and bradykinin. Thimerosal, an InsP₃ receptor-sensitizing compound, enhanced I(hTRP3), but calmidazolium, a calmodulin antagonist, did not affect I(hTRP3). 6. It is concluded that hTRP3 forms non-selective plasmalemmal cation channels that function as a pathway for agonist-induced Ca²⁺ influx.