Effect of inhibition of Na(+)/Ca(2+) exchanger at the time of myocardial reperfusion on hypercontracture and cell death.
OBJECTIVE
There is recent evidence that Ca(2+) influx via reverse mode Na(+)/Ca(2+) exchange (NCX) at the time of reperfusion can contribute to cardiomyocyte hypercontracture. However, forward NCX is essential for normalization of [Ca(2+)](i) during reperfusion, and its inhibition may be detrimental. This study investigates the effect of NCX inhibition with KB-R7943 at the time of reperfusion on cell viability.


METHODS
The effect of several concentrations of KB-R7943 added at reperfusion was studied in Fura-2 loaded quiescent cardiomyocytes submitted to 40 min of simulated ischemia (NaCN 2 mM, pH 6.4), and in rat hearts submitted to 60 min of ischemia. [Ca(2+)](i) and cell length were monitored in myocytes, and functional recovery and LDH release in isolated hearts. From these experiments an optimal concentration of KB-R7943 was identified and tested in pigs submitted to 48 min of coronary occlusion and 2 h of reperfusion.


RESULTS
In myocytes, KB-R7943 at concentrations up to 15 microM reduced [Ca(2+)](i) rise and the probability of hypercontracture during re-energization (P<0.01). Nevertheless, in rat hearts, the effects of KB-R7943 applied during reperfusion after 60 min of ischemia depended on concentration and timing of administration. During the first 5 min of reperfusion, KB-R7943 (0.3-30 microM) induced a dose-dependent reduction in LDH release (half-response concentration 0.29 microM). Beyond 6 min of re-flow, KB-R7943 had no effect on LDH release, except at concentrations > or = 15 microM, which increased LDH. KB-R7943 at 5 microM given during the first 10 min of reflow reduced contractile dysfunction (P=0.011), LDH release (P=0.019) and contraction band necrosis (P=0.014) during reperfusion. Intracoronary administration of this concentration during the first 10 min of reperfusion reduced infarct size by 34% (P=0.033) in pigs submitted to 48 min of coronary occlusion.


CONCLUSIONS
These results are consistent with the hypothesis that during initial reperfusion NCX activity results in net reverse mode operation contributing to Ca(2+) overload, hypercontracture and cell death, and that NCX inhibition during this phase is beneficial. Beyond this phase, NCX inhibition may impair forward mode-dependent Ca(2+) extrusion and be detrimental. These findings may help in the design of therapeutic strategies against lethal reperfusion injury, with NCX as the target.
Inserte
Javier
J
Servicio de Cardiologia, Hospital Universitari Vall d'Hebron, Passeig Vall d'Hebron 119-129, 08035 Barcelona, Spain.
Garcia-Dorado
David
D
Ruiz-Meana
Marisol
M
Padilla
Ferran
F
Barrabés
José A
JA
Pina
Pilar
P
Agulló
Luis
L
Piper
Hans Michael
HM
Soler-Soler
Jordi
J
D000704:Analysis of Variance; D000818:Animals; D002118:Calcium / Q000378:metabolism; D016923:Cell Death / Q000187:drug effects; D048429:Cell Size / Q000187:drug effects; D002478:Cells, Cultured; D004305:Dose-Response Relationship, Drug; D008297:Male; D023421:Models, Animal; D017202:Myocardial Ischemia / Q000378:metabolism / Q000473:pathology*; D015425:Myocardial Reperfusion; D009206:Myocardium / Q000378:metabolism / Q000473:pathology*; D010477:Perfusion; D011897:Random Allocation; D051381:Rats; D017207:Rats, Sprague-Dawley; D012433:Ryanodine / Q000494:pharmacology; D012519:Sarcoplasmic Reticulum / Q000187:drug effects / Q000378:metabolism; D019831:Sodium-Calcium Exchanger / Q000037:antagonists & inhibitors*; D013552:Swine; D019284:Thapsigargin / Q000494:pharmacology; D013890:Thiourea / Q000031:analogs & derivatives* / Q000494:pharmacology*; D013997:Time Factors
C101670:2-(2-(4-(4-nitrobenzyloxy)phenyl)ethyl)isothiourea methanesulfonate; D019831:Sodium-Calcium Exchanger; D012433:Ryanodine; D019284:Thapsigargin; D013890:Thiourea; D002118:Calcium