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Critical Care Research Laboratories, St. Paul's Hospital, University of British Columbia, Vancouver, British Columbia, Canada V6Z 1Y6
Submitted 16 December 2003 ; accepted in final form 8 April 2004
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-
, IL-1
, 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.
intracellular signaling; focal adhesion kinase; Rho; calcium
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