Korean J Physiol Pharmacol.  2013 Oct;17(5):463-468. 10.4196/kjpp.2013.17.5.463.

Disappearance of Hypoxic Pulmonary Vasoconstriction and O2-Sensitive Nonselective Cationic Current in Arterial Myocytes of Rats Under Ambient Hypoxia

• Yoo HY
• Kim SJ

• KMID: 1500243
• DOI: http://doi.org/10.4196/kjpp.2013.17.5.463

Abstract

Acute hypoxia induces contraction of pulmonary artery (PA) to protect ventilation/perfusion mismatch in lungs. As for the cellular mechanism of hypoxic pulmonary vasoconstriction (HPV), hypoxic inhibition of voltage-gated K+ channel (Kv) in PA smooth muscle cell (PASMC) has been suggested. In addition, our recent study showed that thromboxane A2 (TXA2) and hypoxia-activated nonselective cation channel (I(NSC)) is also essential for HPV. However, it is not well understood whether HPV is maintained in the animals exposed to ambient hypoxia for two days (2d-H). Specifically, the associated electrophysiological changes in PASMCs have not been studied. Here we investigate the effects of 2d-H on HPV in isolated ventilated/perfused lungs (V/P lungs) from rats. HPV was almost abolished without structural remodeling of PA in 2d-H rats, and the lost HPV was not recovered by Kv inhibitor, 4-aminopyridine. Patch clamp study showed that the hypoxic inhibition of Kv current in PASMC was similar between 2d-H and control. In contrast, hypoxia and TXA2-activated I(NSC) was not observed in PASMCs of 2d-H. From above results, it is suggested that the decreased I(NSC) might be the primary functional cause of HPV disappearance in the relatively early period (2 d) of hypoxia.

Keyword

Chronic hypoxia; Hypoxic pulmonary vasoconstriction; Nonselective cation channel; O2-sensitive ion channel; Pulmonary artery

MeSH Terms

4-Aminopyridine
Animals
Anoxia*
Lung
Muscle Cells*
Myocytes, Smooth Muscle
Pulmonary Artery
Rats*
Thromboxane A2
Vasoconstriction*
4-Aminopyridine
Thromboxane A2

Figure

• 

  Fig. 1 Comparison of HPV, basal PAP and Ang II-induced ΔPAP between control and 2d-H rats in V/P lungs. (A, B) Representative traces of PAP recording in control (A) and 2d-H rats (B). Hypoxic ventilation (3% PO2)-induced PAP increase (ΔPAPHypox) was abolished in 2d-H. Ang II was initially applied to the perfusate, inducing a transient increase in PAP. (C~E) Summaries of ΔPAPHypoxia (C), basal PAP (D), and AngII-induced ΔPAP (E) are shown as bar graphs comparing the results between control and 2d-H rats (*p<0.05, **p<0.01).

• 

  Fig. 2 Differential structural changes of PAs according to the period of hypoxia in rats. Representative histological figures (H&E staining) of lung from control (A), 2 days of hypoxia (2d-H, B), 2 weeks of hypoxia (2w-H, C), and 3 weeks of hypoxia (3w-H, D). The medial thickness of PA was similar between control and 2d-H, whereas the PAs from 2w-H and 3w-H showed marked hypertropic changes with almost obliterated lumen.

• 

  Fig. 3 Effect of 4-AP, a Kv inhibitor, on PAP and HPV (ΔPAPHypoxia) in control and 2d-H rats. (A, B) Representative traces of PAP recording in control and 2d-H rats. Both basal PAP and ΔPAPHypoxia were increased by 5 mM 4-AP in control (A). In 2d-H, however, basal PAP was slightly increased by 4-AP, and ΔPAPHypoxia was not recovered by the 4-AP pretreatment (B). (C) Summaries of the results shown as bar graphs (n=5; control, n=4; 2d-H, **p<0.01).

• 

  Fig. 4 Effect of acute hypoxia on IKv in PASMCs from control and 2d-H rats. (A, B) Representative current traces obtained by step pulses (between -80 mV and 20 mV, 20 mV interval, 500 ms duration,) from -60 mV of holding potential. The recording was done at 37℃. Acute hypoxia (PO2 3%) decreased the amplitudes of IKv in PASMCs similarly between control and 2d-H PASMCs. (C) Summary of outward current amplitudes at 0 mV normalized to each control (Ctrl-rats; control, H; hypoxia, *p<0.05). The amplitudes of outward currents were measured at the end of step pulses as indicated by downward arrows above (A, B).

• 

  Fig. 5 Effect of acute hypoxia on INSC in PASMCs of control and 2d-H rats. Representative I/V curves of INSC were obtained by ramp pulses (-80 mV~80 mV) with CsCl pipette solution. (A) Application of U46619 alone did not significantly increased INSC, while the additional acute hypoxia significantly increased the conductance. (B) In contrast, INSC was not increased by acute hypoxia in 2d-H rats. Summaries of inward current amplitudes at -60 mV normalized to each control (U; U46619, H; hypoxia) are display as bar graphs in the right panels (**p<0.01).

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