title: Propagation of cardiomyocyte hypercontracture by passage of Na(+) through gap junctions.
abstract: Prolonged ischemia increases cytosolic Ca(2+) concentration in cardiomyocytes. Cells with severely elevated cytosolic Ca(2+) may respond to reperfusion, developing hypercontracture, sarcolemmal disruption, and death. Cardiomyocytes are efficiently connected through gap junctions (GJs) to form a functional syncytium, and it has been shown that hypercontracture can be propagated to adjacent myocytes through a GJ-mediated mechanism. This study investigated the mechanism of propagation of cell injury associated with sarcolemmal rupture in end-to-end connected pairs of isolated rat cardiomyocytes. Microinjection of extracellular medium into one of the cells to simulate sarcolemmal disruption induced a marked increase in cytosolic Ca(2+) (fura-2) and Na(+) (SBFI) in the adjacent cell and its hypercontracture in <30 seconds (22 of 22 cell pairs). This process was not modified when Ca(2+) release from the sarcoplasmic reticulum was blocked with 10 micromol/L ryanodine (5 of 5 cell pairs), but it was fully dependent on the presence of Ca(2+) in the extracellular buffer. Blockade of L-type Ca(2+) channels with 10 micromol/L nifedipine did not alter propagation of hypercontracture. However, the presence of 15 to 20 micromol/L KB-R7943, a highly selective blocker of reverse Na(+)/Ca(2+) exchange, prevented propagation of hypercontracture in 16 of 20 cell pairs (P<0.01) without interfering with GJ permeability, as assessed by the Lucifer Yellow transfer method. Addition of the Ca(2+) chelator EGTA (2 mmol/L) to the injection solution prevented hypercontracture in the injected cell but not in the adjacent one (n=5). These results indicate that passage of Na(+) through GJ from hypercontracting myocytes with ruptured sarcolemma to adjacent cells, and secondary entry of [Ca(2+)](o) via reverse Na(+)/Ca(2+) exchange, can contribute to cell-to-cell propagation of hypercontracture. This previously unrecognized mechanism could increase myocardial necrosis during ischemia-reperfusion in vivo and be the target of new treatments aimed to limit it.
authors.affiliation: Department of Cardiology, Hospital General Universitario Vall d'Hebron, Barcelona, Spain.
authors.forename: M
authors.initials: M
authors.lastname: Ruiz-Meana
authors.forename: D
authors.initials: D
authors.lastname: Garcia-Dorado
authors.forename: B
authors.initials: B
authors.lastname: Hofstaetter
authors.forename: H M
authors.initials: HM
authors.lastname: Piper
authors.forename: J
authors.initials: J
authors.lastname: Soler-Soler
mesh_terms: D000818:Animals; D002118:Calcium / Q000378:metabolism; D002450:Cell Communication / Q000502:physiology; D017629:Gap Junctions / Q000378:metabolism*; D008297:Male; D009200:Myocardial Contraction / Q000502:physiology*; D009206:Myocardium / Q000166:cytology* / Q000378:metabolism*; D009994:Osmolar Concentration; D051381:Rats; D017207:Rats, Sprague-Dawley; D012964:Sodium / Q000378:metabolism*; D019831:Sodium-Calcium Exchanger / Q000502:physiology
chemical_list: D019831:Sodium-Calcium Exchanger; D012964:Sodium; D002118:Calcium