The cardioprotective action of trapidil during ischemia/reperfusion is mediated by restored phosphorylation of phospholamban

Dr. Kaber, Gernot , Prof. Dr. Hohlfeld, Thomas , Prof. Dr. Schrör, Karsten. Universitätsklinikum Düsseldorf Institut für Pharmakologie und Klinische Pharmakologie, Universitätsstr. 1, 40225 Düsseldorf, Germany.

Cytosolic Ca2+-overload is a major cause of damage to myocardial tissue during Ischemia/Reperfusion (I/R). PKA-II dependent phospholamban (PLB) phosphorylation is decreased during I/R and might thereby reduce Ca2+ transport into the sarcoplasmatic reticulum (SR). We have previously shown in rabbits that trapidil (TRA) activates PKA-II and reduces I/R injury. To investigate whether the PKA-II dependent phosphorylation of PLB is responsible for these beneficial effects Langendorff-hearts of wild-type (WT) and phospholamban deficient (PLB-KO) mice were perfused at constant pressure (80 mmHg) and subjected to zero-flow ischemia for 60 min, followed by 45 min of reperfusion (n = 16-18). Hearts were treated with TRA at a concentration that is obtained in clinical use (10µM) or vehicle (VEH). I/R resulted in a significant increase in creatine kinase (CK) release in VEH-treated WT hearts. TRA reduced this effect by more than 60% (p < 0.05). Left ventricular end diastolic pressure (LVEDP) was also elevated in VEH-treated WT hearts, amounting to 39 ± 4 mmHg at the end of reperfusion, and was significantly reduced to 24 ± 4 mmHg by TRA (p < 0.05). PLB-phosphorylation after I/R was significantly improved by TRA and the transport of Ca2+ into the sarcoplasmatic reticulum (SR) was also significantly faster in TRA-treated WT-hearts: 2.8 vs 1.9 counts/µg*min (p < 0.05). No changes were seen in hearts of PLB-KO mice. Treatment with TRA did not alter CK release (1591 ± 219 vs. 1563 ± 155 mU/g*min) nor did it reduce the elevated LVEDP (36 ± 5 vs. 38 ± 5 mmHg) in PLB-KO hearts. There was also no change in Ca2+-uptake by TRA. These data indicate that restauration of PKA-II dependent phosphorylation of PLB by TRA increases Ca2+-uptake into the SR towards normal values and explain the cardioprotective actions of TRA in I/R. This is a novel and injury-specific mechanism of action for a cardioprotective compound.