Accelerated inactivation of cardiac L-type calcium channels triggered by anaesthetic-induced preconditioning.
OBJECTIVE
Cardioprotection against ischaemia by anaesthetic-induced preconditioning (APC) is well established. However, the mechanism underlying Ca(2+) overload attenuation by APC is unknown. The effects of APC by isoflurane on the cardiac L-type Ca channel were investigated.


METHODS
In a model of in vivo APC, Wistar rats were exposed to isoflurane (1.4%), delivered via a vaporizer in an enclosure, prior to thoracotomy. The Dahl S rats were similarly preconditioned to determine strain-dependent effects. Whole-cell patch clamp using cardiac ventricular myocytes was used to determine the L-type Ca(2+) current (I(Ca,L)) characteristics and calmodulin (CaM) levels were determined by Western blot analysis. Cytosolic Ca(2+) levels were monitored using fluo-4-AM. Action potential (AP) simulations examined the effects of APC.


RESULTS
In Wistar rats, APC significantly accelerated I(Ca,L) inactivation kinetics. This was abolished when external Ca(2+) was replaced with Ba(2+), suggesting that Ca(2+)-dependent inactivation of I(Ca,L) was modulated by APC. Expression levels of CaM, a determinant of I(Ca,L) inactivation, were not affected. Attenuation of cytosolic Ca(2+) accumulation following oxidative stress was observed in the APC group. Simulations showed that the accelerated inactivation of I(Ca,L) resulted in a shortening of the AP duration. The Dahl S rat strain was resistant to APC and changes in I(Ca,L) inactivation were not observed in cardiomyocytes prepared from these rats.


CONCLUSIONS
APC triggered persistent changes in the inactivation of cardiac L-type Ca channels. This can potentially lead to a reduction in Ca(2+) influx and attenuation of Ca(2+) overload during ischaemia/reperfusion.
Tampo
A
A
Department of Anesthesiology, Medical College of Wisconsin, Milwaukee, 53226, USA.
Hogan
C S
CS
Sedlic
F
F
Bosnjak
Z J
ZJ
Kwok
W M
WM
D018685:Anesthetics, Inhalation / Q000494:pharmacology*; D000818:Animals; D001464:Barium / Q000378:metabolism; D015153:Blotting, Western; D002118:Calcium / Q000378:metabolism*; D020746:Calcium Channels, L-Type / Q000378:metabolism*; D002470:Cell Survival / Q000187:drug effects; D002478:Cells, Cultured; D003600:Cytosol / Q000378:metabolism; D006352:Heart Ventricles / Q000378:metabolism; D015640:Ion Channel Gating / Q000187:drug effects; D019157:Ischemic Preconditioning, Myocardial; D007530:Isoflurane / Q000494:pharmacology*; D008297:Male; D032383:Myocytes, Cardiac / Q000378:metabolism*; D018384:Oxidative Stress / Q000187:drug effects; D018408:Patch-Clamp Techniques; D051381:Rats; D020303:Rats, Inbred Dahl; D017208:Rats, Wistar
D018685:Anesthetics, Inhalation; D020746:Calcium Channels, L-Type; D001464:Barium; D007530:Isoflurane; D002118:Calcium