title: Novel regulatory mechanism of cardiomyocyte contractility involving ICAM-1 and the cytoskeleton.
abstract: ICAM-1 mediates interaction of cardiomyocytes with the extracellular matrix and leukocytes and may play a role in altering contractility. To investigate this possibility, rat ventricular cardiomyocytes were activated using TNF-alpha, IL-1beta, or LPS, washed, cultured with quiescent rat polymorphonuclear leukocytes (PMNs) for 4 h, and electrically stimulated to determine fractional shortening. PMNs cultured with activated cardiomyocytes reduced control fractional shortening of 20.5 +/- 0.7% by -2.8 +/- 0.3% per adherent PMN (P < 0.001). Fixing PMNs with paraformaldehyde or glutaraldehyde did not prevent PMN-mediated decreases in cardiomyocyte fractional shortening. However, PMN adherence and decreased fractional shortening were prevented by anti-ICAM-1 and anti-CD18 antibodies. Reduced fractional shortening was reproduced in the absence of PMNs by ICAM-1 binding using cross-linking antibodies (reduced by 36 +/- 3% from control, P < 0.01). Immunofluorescent staining demonstrated increased cortical cytoskeleton-associated focal adhesion kinase expression after ICAM-1 cross-linking, suggesting involvement of the actin cytoskeleton. Indeed, disruption of F-actin filament assembly using cytochalasin D or latrunculin A did not prevent PMN adherence but prevented decreased fractional shortening. Inhibition of the cytoskeleton-associated Rho-kinase pathway with HA-1077 prevented ICAM-1-mediated decreases in cardiomyocyte contractility, further suggesting a central role of the actin cytoskeleton. Importantly, ICAM-1 cross-linking did not alter the total intracellular Ca2+ transient during cardiomyocyte contraction but greatly increased heterogeneity of intracellular Ca2+ release. Thus we have identified a novel regulatory mechanism of cardiomyocyte contractility involving the actin cytoskeleton as a central regulator of the normally highly coordinated pattern of sarcoplasmic Ca2+ release. Cardiomyocyte ICAM-1 binding, by PMNs or other ligands, induces decreased cardiomyocyte contractility via this pathway.
authors.affiliation: Critical Care Research Laboratories, St. Paul's Hospital, University of British Columbia, Vancouver, Canada V6Z 1Y6.
authors.forename: Ehsan Y
authors.initials: EY
authors.lastname: Davani
authors.forename: Delbert R
authors.initials: DR
authors.lastname: Dorscheid
authors.forename: Cheng-Han
authors.initials: CH
authors.lastname: Lee
authors.forename: Cornelis
authors.initials: C
authors.lastname: van Breemen
authors.forename: Keith R
authors.initials: KR
authors.lastname: Walley
mesh_terms: D000199:Actins / Q000502:physiology; D000818:Animals; D002118:Calcium / Q000378:metabolism; D002448:Cell Adhesion / Q000502:physiology; D002478:Cells, Cultured; D018920:Coculture Techniques; D003599:Cytoskeleton / Q000502:physiology*; D018799:Intercellular Adhesion Molecule-1 / Q000378:metabolism / Q000502:physiology*; D008297:Male; D009200:Myocardial Contraction / Q000502:physiology*; D032383:Myocytes, Cardiac / Q000502:physiology*; D009504:Neutrophils / Q000378:metabolism / Q000502:physiology; D051381:Rats; D017207:Rats, Sprague-Dawley; D015398:Signal Transduction / Q000502:physiology
chemical_list: D000199:Actins; D018799:Intercellular Adhesion Molecule-1; D002118:Calcium