Preservation of myofilament calcium responsiveness underlies protection against myocardial stunning by ischemic preconditioning.

Pérez N G, Marbán E, Cingolani H E

Department of Medicine, Johns Hopkins University School of Medicine, Baltimore, MD 21205, USA.

Cardiovasc Res. 1999 Jun;42(3):636-43. doi: 10.1016/s0008-6363(98)00299-5.

OBJECTIVE

Whereas diminution of infarct size by ischemic preconditioning (IP) is well-accepted, protection against stunning is controversial. Since stunning is characterized by decreased myofilament Ca2+ responsiveness, we investigated whether IP would preserve myofilament responsiveness in a model of stunning.

METHODS

Rat hearts were retrogradely perfused with Krebs-Henseleit (K-H) solution for 20 min and then subjected to 20 min of no-flow global ischemia, followed by 20 min of reperfusion in the absence (stunning) or in the presence (IP) of a previous 5-min period of ischemia followed by 15 min of reperfusion. A group of hearts perfused under non-ischemic conditions served as control. Thin ventricular trabeculae were dissected from each of the experimental groups and loaded with fura-2 to measure intracellular calcium concentration ([Ca2+]i) and developed force.

RESULTS

After 20 min of reperfusion, left ventricular developed pressure decreased in stunned hearts to 61 +/- 5% of control (P < 0.01), whereas recovery was complete in the IP hearts (97 +/- 4%). Steady-state [Ca2+]i-force relationships revealed a decreased maximal Ca(2+)-activated force in stunned hearts relative to control, but no change in the IP group. The Ca2+ required for 50% activation increased in stunning but not in IP.