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 pul monary artery endothelial (CPAE) cells, which do not express the bovine trp 3 isoform (btrp3) but express btrp1 and btrp4. 2. ATP, bradykinin and intracellular InsP(3) activated a non-selective cati on current (I-hTRP3) in htrp3-transfected CPAE cells but not in non-transfe cted wild-type cells. During agonist stimulation, the sustained rise in [Ca 2+](i) was significantly higher in htrp3-transfected cells than in control CPAE cells. 3. The permeability for monovalent cations was P-Na > P-Cs approximate to 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+ w ere potent blockers of I-hTRP3 (the IC50 for La3+ was 24.4 +/- 0.7 mu M). 4. The single-channel conductance of the channels activated by ATP, assesse d by noise analysis, was 23 pS. 5. Thapsigargin and 2,5-di-tertbutyl-1,4-benzohydroquinone (BHQ), inhibitor s of the organellar Ca2+-ATPase, failed to activate I-hTRP3. U-73122, a pho spholipase C blocker, inhibited I-hTRP3 that had been activated by ATP and bradykinin. Thimerosal, an InsP(3) 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 chann els that function as a pathway for agonist-induced Ca2+ influx.