Effects Of Induced Post-ischemic Phosphorylation On Action Potential Propagation In Mouse Neonatal Cardiomyocytes

Abstract

Intracellular events triggered by protein phosphorylation and kinase translocation have been reported to help preventing larger cardiac tissue damage. Our objective was to determine if immediate changes in phosphorylation post-infarction, resembling clinical treatments could affect conduction velocity and further cardiac protection.Cardiomyocytes from 0-2 day old mice pups were grown on 64 Micro-Electrode Arrays (MEAs; MES, Germany). The MEAs recorded action potential (AP) propagation produced by neonatal cardiomyocytes isolated and culture for 2 days. Myocytes were subjected to ischemia by placing a 13mm glass round cover-slip over the preparation for 45 minutes and recordings were made during and after cover-slip removal. After the ischemic event, random groups were treated with 300nM TPA to induce phosphorylation for one hour. TPA was removed and both groups were incubated for 24 hours. Following incubation cells were subjected to another ischemic event. Recordings were done after the ischemic event and again thirty minutes later. Conduction velocity (CV) was averaged from all electrodes.Phosphorylation and kinase translocation has been known to protect cardiocytes during ischemic preconditioning. We now present conditions where phosphorylation can actually be detrimental if induced after an ischemic event. At the 24 hour point, the control group had recovered AP CV by 99±2% (mean±SE) compared to the TPA treated group which recovered to 56±8%. The TPA treated group then showed only an average of 14±7% decrease in AP CV and AP amplitude upon administering the second ischemic event whereas the control group AP CV decreased by an average of 55%±9. When induced early after an ischemic event, phosphorylation results protective to maintain CV but appears to become detrimental for cellular survival.