Classical transient receptor potential channel 6 (TRPC6) is essential for hypoxic pulmonary vasoconstriction and alveolar gas exchange

Abstract

Regional alveolar hypoxia causes local vasoconstriction in the lung, shifting blood flow from hypoxic to normoxic areas, thereby maintaining gas exchange. This mechanism is known as hypoxic pulmonary vasoconstriction (HPV). Disturbances in HPV can cause life-threatening hypoxemia whereas chronic hypoxia triggers lung vascular remodeling and pulmonary hypertension. The signaling cascade of this vitally important mechanism is still unresolved. Using transient receptor potential channel 6 (TRPC6)-deficient mice, we show that this channel is a key regulator of acute HPV as this regulatory mechanism was absent in TRPC6 ؊/؊ mice whereas the pulmonary vasoconstrictor response to the thromboxane mimetic U46619 was unchanged. Accordingly, induction of regional hypoventilation resulted in severe arterial hypoxemia in TRPC6 ؊/؊ but not in WT mice. This effect was mirrored by a lack of hypoxiainduced cation influx and currents in smooth-muscle cells from precapillary pulmonary arteries (PASMC) of TRPC6 ؊/؊ mice. In both WT and TRPC6 ؊/؊ PASMC hypoxia caused diacylglycerol (DAG) accumulation. DAG seems to exert its action via TRPC6, as DAG kinase inhibition provoked a cation influx only in WT but not in TRPC6 ؊/؊ PASMC. Notably, chronic hypoxia-induced pulmonary hypertension was independent of TRPC6 activity. We conclude that TRPC6 plays a unique and indispensable role in acute hypoxic pulmonary vasoconstriction. Manipulation of TRPC6 function may thus offer a therapeutic strategy for the control of pulmonary hemodynamics and gas exchange.hypoxia-induced diacylglycerol accumulation ͉ precapillary pulmonary arterial smooth-muscle cells ͉ pulmonary hypertension ͉ transient receptor potential channel 6-deficient mouse model ͉ arterial hypoxemia A cute regional hypoxic pulmonary vasoconstriction (HPV) is necessary to maintain optimized gas exchange by directing blood flow from poorly ventilated to well ventilated areas of the lung. Under conditions of generalized hypoxia, however, total pulmonary vascular resistance rises with subsequent increase of right heart load (1-3). Chronic hypoxia, as occurring in ventilatory disorders induces chronic pulmonary hypertension, pulmonary vascular remodeling, and cor pulmonale (4). The underlying oxygen sensing and signal transduction mechanisms of the acute and chronic vascular responses are largely unknown. A rise of intracellular calcium ([Ca 2ϩ ] i ) in pulmonary artery smooth-muscle cells (SMCs) has been suggested to be the key event in these processes (5-8). However, the question how [Ca 2ϩ ] i is regulated has not yet been resolved. Among others, transient receptor potential (TRP) channels are regulators of [Ca 2ϩ ] i . The TRP protein superfamily consists of a diverse group of nonselective cation channels involved in many basic cellular processes (9). Whereas members of the TRPV and TRPM subfamilies have emerged as versatile cellular sensors, the functional importance of the seven members (TRPC1 to -7) of the TRPC (transient receptor potential cation channel subfamily C) subfamily...

Superoxide Generated at Mitochondrial Complex III Triggers Acute Responses to Hypoxia in the Pulmonary Circulation

“…This attenuation suggests that Complex III is required for hypoxic ROS signaling in diverse vascular cell types, and it is not consistent with the observation by Michelakis and colleagues (24) that SASMC mitochondria behave reciprocally to PASMC in terms of ROS generation during hypoxia. In PASMC, hypoxia elicits increases in [Ca 21 ] i to cause vasoconstriction (42)(43)(44)(45)(46)(47), whereas SASMC decrease [Ca 21 ] i and undergo relaxation (24,48,49). Our observation that RISP depletion in SASMC has no detectable effect on calcium signaling ( Figure 5B) Figure 4A).…”

Regulation of hypoxic pulmonary vasoconstriction: basic mechanisms

“…The ROCs can be activated by protein kinases and diacylglycerol. Recently, the present authors have demonstrated that this mechanism is indispensable for acute HPV, occurring within seconds to minutes, as: 1) TRPC6 knockout mice have no pulmonary vascular reactivity to hypoxia although they fully respond to nonhypoxia induced vasoconstriction; and 2) PASMCs isolated from TRPC6-deficient mice exhibit no hypoxic calcium increase and membrane current when exposed to hypoxia, in contrast to wild-type PASMCs [54]. TRPC6 may modulate intracellular calcium and membrane potential by subsequent gating of K v and L-type calcium channels.…”

Expression and function of soluble guanylate cyclase in pulmonary arterial hypertension

“…The isolated perfused lung model has previously been described in detail [19] (refer to the online supplementary data).…”

“…Mice were exposed to chronic hypoxia (10% O 2 ) in a ventilated chamber, as described previously [18,19]. Rats were injected with 60 mg?kg -1 monocrotaline (MCT) subcutaneously [18][19][20].…”