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.
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