The role of classical transient receptor potential channels in the regulation of hypoxic pulmonary vasoconstriction.

Hypoxic pulmonary vasoconstriction (HPV) is an essential mechanism of the lung matching blood perfusion to ventilation during local alveolar hypoxia. HPV thus optimizes pulmonary gas exchange. In contrast chronic and generalized hypoxia leads to pulmonary vascular remodeling with subsequent pulmonary hypertension and right heart hypertrophy. Among other non-selective cation channels, the family of classical transient receptor potential channels (TRPC) has been shown to be expressed in pulmonary arterial smooth muscle cells. Among this family, TRPC6 is essential for the regulation of acute HPV in mice. Against this background, in this chapter we give an overview about the TRPC family and their role in HPV.

Loss of classical transient receptor potential 6 channel reduces allergic airway response.

BACKGROUND: Non-selective cation influx through canonical transient receptor potential channels (TRPCs) is thought to be an important event leading to airway inflammation. TRPC6 is highly expressed in the lung, but its role in allergic processes is still poorly understood. OBJECTIVE: The purpose of this study was to evaluate the role of TRPC6 in airway hyperresponsiveness (AHR) and allergic inflammation of the lung. METHODS: Methacholine-induced AHR was assessed by head-out body plethysmography of wild type (WT) and TRPC6(-/-) mice. Experimental airway inflammation was induced by intraperitoneal ovalbumin (OVA) sensitization, followed by OVA aerosol challenges. Allergic inflammation and mucus production were analysed 24 h after the last allergen challenge. RESULTS: Methacholine-induced AHR and agonist-induced contractility of tracheal rings were increased in TRPC6(-/-) mice compared with WT mice, most probably due to compensatory up-regulation of TRPC3 in airway smooth muscle cells. Most interestingly, when compared with WT mice, TRPC6(-/-) mice exhibited reduced allergic responses after allergen challenge as evidenced by a decrease in airway eosinophilia and blood IgE levels, as well as decreased levels of T-helper type 2 (Th2) cytokines (IL-5, IL-13) in the bronchoalveolar lavage. However, lung mucus production after allergen challenge was not altered by TRPC6 deficiency. CONCLUSIONS: TRPC6 deficiency inhibits specific allergic immune responses, pointing to an important immunological function of this cation channel in Th2 cells, eosinophils, mast cells and B cells.

TRPC channels in vascular cell function.

The mammalian transient receptor potential (TRP) superfamily of non-selective cation channels can be divided into six major families. Among them, the "classical" or "canonical" TRPC family is most closely related to Drosophila TRP, the founding member of the superfamily. All seven channels of this family designated TRPC1-7 share the common property of receptor-operated activation through phospholipase C (PLC)-coupled receptors, but their regulation by store-dependent mechanisms involving the proteins STIM and ORAi is still discussed controversially. This review will focus on the proposed functions of TRPC proteins in cells of the vascular system (e.g. platelets, smooth muscle cells and endothelial cells) and will present data concerning their physiological functions analysed in isolated tissues with down-regulated channel activity and in gene-deficient mouse models.