Korean J Physiol Pharmacol.  2012 Feb;16(1):59-64. 10.4196/kjpp.2012.16.1.59.

Requirement of Pretone by Thromboxane A2 for Hypoxic Pulmonary Vasoconstriction in Precision-cut Lung Slices of Rat

• Park SJ
• Yoo HY
• Kim HJ
• Kim JK
• Zhang YH
• Kim SJ

• KMID: 2285441
• DOI: http://doi.org/10.4196/kjpp.2012.16.1.59

Abstract

Hypoxic pulmonary vasoconstriction (HPV) is physiologically important response for preventing mismatching between ventilation and perfusion in lungs. The HPV of isolated pulmonary arteries (HPV-PA) usually require a partial pretone by thromboxane agonist (U46619). Because the HPV of ventilated/perfused lungs (HPV-lung) can be triggered without pretone conditioning, we suspected that a putative tissue factor might be responsible for the pretone of HPV. Here we investigated whether HPV can be also observed in precision-cut lung slices (PCLS) from rats. The HPV in PCLS also required partial contraction by U46619. In addition, K+ channel blockers (4AP and TEA) required U46619-pretone to induce significant contraction of PA in PCLS. In contrast, the airways in PCLS showed reversible contraction in response to the K+ channel blockers without pretone conditioning. Also, the airways showed no hypoxic constriction but a relaxation under the partial pretone by U46619. The airways in PCLS showed reliable, concentration-dependent contraction by metacholine (EC50, ~210 nM). In summary, the HPV in PCLS is more similar to isolated PA than V/P lungs. The metacholine-induced constriction of bronchioles suggested that the PLCS might be also useful for studying airway physiology in situ.

Keyword

Lung slice; Hypoxic pulmonary vasoconstriction; Thromboxane A2; Airway smooth muscle

MeSH Terms

15-Hydroxy-11 alpha,9 alpha-(epoxymethano)prosta-5,13-dienoic Acid
Animals
Bronchioles
Constriction
Contracts
Lung
Perfusion
Pulmonary Artery
Rats
Relaxation
Thromboplastin
Thromboxane A2
Vasoconstriction
Ventilation
15-Hydroxy-11 alpha,9 alpha-(epoxymethano)prosta-5,13-dienoic Acid
Thromboplastin
Thromboxane A2

Figure

• 

  Fig. 1 Essential role of TXA2 on HPV in PAs. (A) Hypoxia (3% Po2) alone did not induce an increased tension of PAs. (B) In the presence of U46619 (10 nM), a strong contraction of PAs occurred in response to hypoxia. (C) Summaries of PAs tone normalized to 80K-induced contraction were shown as a bar graph (mean±SEM, n=7). *Indicates statistically significant difference from the control value (p<0.05). (D) Induction of HPV in V/P lungs. The increase in pulmonary arterial pressure (PAP, mmHg) was observed by hypoxic ventilation. In the same lung, Ang II induced a transient PAP increase, which augmented the HPV response. (E) A pretreatment with U46619 also induced a transient PAP increase, and HPV was also observed afterwards.

• 

  Fig. 2 Identification of PA and AW constrictions in rat PCLS. (A) A representative image of rat PCLS demonstrating the AW and PA. (B) Functional discrimination of PA and AW according to differential responses to ACh and K+ channel blockers. AW showed strong constriction to ACh (10 µM), tetraethylammonium (TEA, 2 mM) and 4-aminopyridine (4AP, 5 mM) while PA showed no response to the concomitant application of the above agents.

• 

  Fig. 3 Responses of PA to hypoxia and K+ channel blockers under pretone conditions in rat PCLS. Three representative cases of relative luminal area (% initial area) changes in PAs. In all cases (A~C), the K+ channel blockers (TEA and 4AP) induced reversible constriction only under the pretreatment with 5 nM U46619 while not with 100 nM Ang II (B). Also, the hypoxic constriction was observed under the pretreatment with 5 nM U46619 (A, C).

• 

  Fig. 4 Responses of AW to hypoxia and K+ channel blockers under pretone conditions in rat PCLS. Two representative cases of luminal area (% initial area) changes in AWs. The strong contractile response to 10 µM ACh was confirmed along with the response to 60 K. Hypoxia alone had no effect (A) or induced a slight dilation (B) of AW. Application of 5 nM U46619 induced oscillatory or tonic constrictions that were not affected (A) or partly inhibited by hypoxia (B). Different from PAs, both 4AP and TEA induced constriction of AW in the absence of U46619 pretreatment.

• 

  Fig. 5 Response of AW to metacholine (MCh) in mouse PCLS. (A) A representative image of rat PCLS demonstrating the AW and PA. Note the relatively narrow lumen of PA in the mouse PCLS. (B) Concentration-dependent reversible constrictions of mouse AW. The maximum constriction induced by 100 µM MCh was markedly larger (>five fold) than the 60K-constriction. (C) Normalized AW constrictions to different concentrations of MCh were averaged and fitted to logistic functions. Each panel was obtained by different type of normalization criteria; relative change from the maximum luminal area (left), normalized against 60K constriction (middle), and normalized to maximum constriction by 100 µM MCh (right). Regardless of the normalization criteria, the half-effective concentration (EC50) of MCh located at similar ranges.

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