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Aortic smooth muscle and endothelial plasma membrane Ca2+ pump isoforms are inhibited differently by the

Jyoti Pande1, Kanwaldeep K Mallhi, Ahilya Sawh

  • 1Department of Medicine, HSC 4N41, McMaster University, 1200 Main St. West, Hamilton, Ontario L8N 3Z5, Canada.

American Journal of Physiology. Cell Physiology
|February 3, 2006
PubMed

Insights

A novel peptide, caloxin 1b1, selectively inhibits plasma membrane calcium ATPases (PMCA) extracellularly. This inhibitor shows greater potency for PMCA4 in smooth muscle than PMCA1 in endothelium, impacting vascular tone.

Area of Science:

  • Biochemistry
  • Molecular Biology
  • Cardiovascular Physiology

Background:

  • Plasma membrane Ca(2+) pumps (PMCA) regulate cellular calcium levels.
  • PMCA isoforms (PMCA1-4) exhibit differential expression in vascular tissues.
  • Endothelium predominantly expresses PMCA1, while smooth muscle expresses PMCA4 and PMCA1.

Purpose of the Study:

  • To identify and characterize a novel extracellular inhibitor of PMCA isoforms.
  • To investigate the isoform selectivity and potency of the inhibitor.
  • To examine the effects of the inhibitor on vascular smooth muscle and endothelium.

Main Methods:

  • Screening for peptides binding to the extracellular domain of PMCA4.
  • Assessing PMCA Ca(2+)-Mg(2+)-ATPase activity inhibition in erythrocyte ghosts and HEK-293 cells.
  • Evaluating the effects of the inhibitor on isometric tension in aortic rings (with and without endothelium).
  • Measuring cytosolic Ca(2+) in cultured vascular smooth muscle and endothelial cells.

Main Results:

  • A novel peptide, caloxin 1b1, was identified with high affinity for PMCA4.
  • Caloxin 1b1 selectively inhibited PMCA4 (K(i) = 46 μM) more potently than PMCA1 (K(i) = 105 μM).
  • Caloxin 1b1 induced contraction in de-endothelialized aortic rings and increased phenylephrine-induced contraction.
  • In intact aortic rings, caloxin 1b1 increased contraction, not endothelium-dependent relaxation.
  • Caloxin 1b1 increased cytosolic Ca(2+) more in smooth muscle cells than endothelial cells.

Conclusions:

  • Caloxin 1b1 is the first highly selective extracellular PMCA inhibitor.
  • The inhibitor demonstrates greater efficacy on vascular smooth muscle than on endothelium.
  • Caloxin 1b1 provides a novel tool for studying PMCA function in vascular physiology.

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