Proceedings of The Physiological Society
University of Oxford (2011) Proc Physiol Soc 23, PC358
Evidence of phosphatidylcholine-specific phospholipase C involvement in hypoxic pulmonary vasoconstriction
I. V. Strielkov1, J. P. Ward2, P. I. Aaronson2
1. Department of Experimental therapeutics, Intitute of pharmacology and toxicology of AMN of Ukraine, Kyiv, Ukraine. 2. Department of Physiology, King’s College, London, United Kingdom.
The intrinsic mechanisms underlying hypoxic pulmonary vasoconstriction (HPV) are still poorly understood. Data obtained to date indirectly point towards the possible involvement of phosphatidylcholine-specific phospholipase C (PC-PLC) in this phenomenon (Witzenrath et al., 2006; Cheng et al., 2006). PC-PLC hydrolyzes phosphatidylcholine to phosphocholine and diacylglycerol which activates conventional and novel isoforms of protein kinase C, and certain non-selective ion channels, notably TRPC6. The aim of this study was to test the hypothesis that PC-PLC activation during hypoxia contributes to development of HPV. Contractile force was measured using the wire myograph technique in rat small intrapulmonary arteries (IPA) preconstricted with U46619 (20-220 nM), or in the absence of preconstriction. In vivo experiments were performed on rats with retrograde catheterization of the right ventricle and the left common carotid artery for systolic right ventricular pressure (RVP) and arterial pressure recording. Animals were anesthetized with chloralose/urethane (i.p.; 80 and 800 mg/kg respectively). Hypoxic hypoxia in in vivo was achieved by mechanical ventilation with a gas mixture containing 10% O2 in N2. Hypoxia induced a biphasic contraction in preconstricted IPA. The transient phase (phase I) amounted to 44.2 ± 6.0% of the contraction elicited by 80 mM K+ (TK) (n = 7), and the sustained phase (phase II) reached 16.4 ± 5.6% of TK. Inhibition of PC-PLC with D609 (30 µM) diminished phase I by 67% (to 14.6 ± 1.8% TK, p < 0.01) and abolished the sustained phase (-6.6 ± 0.6% TK, p < 0.01). Hypoxia induced a small but significant contraction in IPA in the absence of preconstriction, though the phases were not clearly separable (5.0 ± 0.6% TK, p < 0.01, n = 7). D609 suppressed HPV in the absence of preconstriction by 60% (2.0 ± 0.7% TK, p < 0.01). Conversely, inhibition of phosphatidylinositol-specific phospholipase C with U-73122 (3 µM) did not affect HPV in IPA in the absence of preconstriction (p > 0.05, n = 6). Hypoxia also provoked a biphasic increase in RVP in experiments in vivo, with maximum RVP rising from 29.7 ± 1.1 mmHg to a transient of 41.7 ± 1.2 mmHg and a sustained value of 39.2 ± 1.3 mmHg (p < 0.01 for both phases, n = 10). Intravenous injection of D609 (5 mg/kg) 30 min before hypoxia prevented the development of the pulmonary hypertension (33.1 ± 1.8 mmHg, p > 0.05, n = 10). D609 did not affect changes in systemic blood pressure in hypoxia. In conclusion, the results suggest that PC-PLC may be of importance in the development of both phases of HPV, but with a greater role in sustained HPV.
Where applicable, experiments conform with Society ethical requirements