Voltage-gated K⁺-channel activity in ovine pulmonary vasculature is developmentally regulated

Abstract

To examine mechanisms underlying developmental changes in pulmonary vascular tone, we tested the hypotheses that 1) maturation-related changes in the ability of the pulmonary vasculature to respond to hypoxia are intrinsic to the pulmonary artery (PA) smooth muscle cells (SMCs); 2) voltage-gated K(+) (K(v))-channel activity increases with maturation; and 3) O(2)-sensitive Kv2.1 channel expression and message increase with maturation. To confirm that maturational differences are intrinsic to PASMCs, we used fluorescence microscopy to study the effect of acute hypoxia on cytosolic Ca(2+) concentration ([Ca(2+)](i)) in SMCs isolated from adult and fetal PAs. Although PASMCs from both fetal and adult circulations were able to sense an acute decrease in O(2) tension, acute hypoxia induced a more rapid and greater change in [Ca(2+)](i) in magnitude in PASMCs from adult compared with fetal PAs. To determine developmental changes in K(v)-channel activity, the effects of the K(+)-channel antagonist 4-aminopyridine (4-AP) were studied on fetal and adult PASMC [Ca(2+)](i). 4-AP (1 mM) caused PASMC [Ca(2+)](i) to increase by 94 +/- 22% in the fetus and 303 +/- 46% in the adult. K(v)-channel expression and mRNA levels in distal pulmonary arteries from fetal, neonatal, and adult sheep were determined through the use of immunoblotting and semiquantitative RT-PCR. Both Kv2.1-channel protein and mRNA expression in distal pulmonary vasculature increased with maturation. We conclude that there are maturation-dependent changes in PASMC O(2) sensing that may render the adult PASMCs more responsive to acute hypoxia.

Abnormal Balance in the Angiopoietin-Tie2 System in Human Brain Arteriovenous Malformations

“…2,11,12 Primer sets for Ang1, Ang2, and Tie2 were from R&D Systems. Primary antibodies against Ang1 and Ang2 were provided by Regeneron Pharmaceutical (Tarrytown, NY).…”

Molecular physiology of oxygen-sensitive potassium channels

“…The expression of Kv2.1 was subsequently demonstrated by Western blot analysis in rat and ovine PA myocytes [42 -44]. Interestingly, the increase in Kv2.1 channel activity parallels the increase in hypoxic pulmonary vasoconstriction that occurs with maturation in ovine pulmonary vasculature [42]. Both the Kv2.1 homomultimer and the Kv2.1/Kv9.3 heteromultimer are reversibly inhibited by hypoxia when expressed in COS and L cells [40,45].…”

Prenatal Programming of Pulmonary Hypertension Induced by Chronic Hypoxia or Ductal Ligation in Sheep

“…69 Inhibition of K v is an important component of the membrane depolarization process. 149,150 These K v channels help maintain a negative resting membrane potential and are important to the vasoconstrictive response with acute hypoxia. 69 Suppressing K v channel activity depolarizes the membrane, which elicits Ca 2+ signals that cause myocyte contraction.…”