Capsaicin‐sensitive TRPV1 Currents Are Enhanced in Pulmonary Artery Smooth Muscle Cells from Patients with Pulmonary Arterial Hypertension

Abstract

Listen

Translate article

Pulmonary arterial hypertension (PAH) is a fatal and progressive disease. Sustained pulmonary vasoconstriction and excessive pulmonary vascular remodeling are two major causes for elevated pulmonary vascular resistance and pulmonary arterial pressure in patients with PAH. Ca2+ signaling in pulmonary artery smooth muscle cells (PASMC) plays a central role in the development and progression of PAH as it is involved with both vasoconstriction, by triggering PASMC contraction, and vascular remodeling, via stimulation of PASMC proliferation. Enhanced Ca2+ signaling has been observed in PASMCs from patients with PAH and is due in part to increased Ca2+ influx through upregulated plasmalemmal Ca2+‐permeable channels. Several members of the transient receptor potential (TRP) channel family are known to facilitate Ca2+ entry. TRP channels are relatively nonselective cation channels consisting of six subfamilies, including the vanilloid (TRPV) ion channels. TRPV1 channels respond to physical stimulus such as noxious temperatures as well as ligand stimuli like capsaicin. TRPV1 is expressed in PASMCs and has been implicated in vascular remodeling and possibly vasoconstriction of the pulmonary artery. However, TRPV1 currents have not been fully characterized in PASMCs. To study this, we used the patch clamp technique to measure capsaicin‐induced single‐channel currents in PASMCs in cell‐attached mode and to investigate whether channel activity is altered in PASMC from idiopathic PAH (IPAH) patients. Under conditions where membrane potential was set to ~0 mV (using high K+ bath solution), channel openings were detected with reversal potential of −3.49 mV and −3.57 mV for normal PASMCs and IPAH‐PASMCs, respectively, in the presence of capsaicin (1 μM). The TRPV1 antagonist capsazepine (10 μM) decreased the steady‐state open probability (Popen) of the single‐channel currents without altering the amplitude of the currents. The slope conductance for normal and IPAH PASMCs was 131 pS and 135 pS, respectively. To rule out any potential influence from other channels, we used an inhibitor cocktail consisting of paxilline and apamin (Ca2+‐activated K+ channel blockers), tetraethylammonium (voltage‐gated K+ channel blocker), and niflumic acid (Cl− channel inhibitor) in the pipette solution. Under these conditions, the open probability of capsaicin‐activated single‐channel currents was markedly enhanced, compared to the vehicle groups for IPAH‐PASMCs. In addition, Western blot studies indicated that the protein expression level of TRPV1 in IPAH‐PASMCs was greater than in normal PASMCs.. Taken together, these data suggest that upregulated expression of TRPV1 channels is associated with the increased Popen of capsaicin‐activated single channel currents in IPAH‐PASMC compare to normal PASMC. This could explain, in part, the enhancement of Ca2+ influx observed in PASMCs from IPAH patients.Support or Funding InformationResearch supported by NIH Grants (HL115014, HL066012 and HL098053).