Objective: The neonate is at high risk of developing pulmonary hypertension, which may reflect a misbalance between vasodilator and vasoconstrictor agents. Thromboxane A(2) (TXA(2)) is involved in several forms pulmonary hypertension, but the signaling pathways mediating its pulmonary vasoconstrictor responses during postnatal maturation have not been analyzed. We therefore investigated the role of L-type Ca(2+) channels, protein kinase C (PKC) zeta, voltage-gated K(+) channels (K(V)), and RhoA/Rho kinase in TXA(2)-induced pulmonary vasoconstriction during postnatal maturation.
Methods: Changes in contractility and intracellular calcium were analyzed in 1 day (newborn) and 2-week-old piglets' pulmonary arteries (PA). K(V) currents were investigated in freshly isolated smooth muscle cells using the whole-cell configuration of the patch clamp technique.
Results: The contractile responses to the TXA(2) mimetic U46619 were similar at both ages but the L-type Ca(2+) channel blocker nifedipine and a PKCzeta pseudosubstrate inhibitor only attenuated the contraction in newborn PA. K(V) currents were similarly inhibited by U46619, although their density was dramatically reduced in 2-week-old as compared to newborn PA smooth muscle cells. This was consistent with a greater contraction to the K(V) inhibitor, 4-aminopyridine, and with a leftward shift in the increase in intracellular Ca(2+) by U46619 in newborn versus older animals. On the other hand, the Rho kinase inhibitor Y-27632 induced a stronger inhibitory effect on the contraction induced by U46619 in 2-week-old than in newborn PA and this was accompanied with minor effects on intracellular calcium levels.
Conclusion: TXA(2)-induced pulmonary vasoconstriction involves PKCzeta-K(V)-L-type Ca(2+) channel and RhoA/Rho kinase signaling pathways, which are downregulated and upregulated, respectively, during postnatal maturation. The different contribution of these pathways could be of relevant importance for the vasodilator therapy choice in the treatment of pulmonary hypertension.