Abstract 1790: New Strategy to Protect Coronary Endothelium from Ischemia-Reperfusion Injury in Cardiac Surgery by using Ca2+-activated K+ Channel Activator (1-Ethyl-2-benzimidazolinone [EBIO]): Cellular Electrophysiological and Mechanical Studies
Introduction & Hypothesis Coronary circulation contributes greatly to post-operative cardiac performance and ischemia-reperfusion (I-R) injury to endothelium is a known cause of endothelial dysfunction. We tested the hypothesis that intermediate conductance Ca2+-activated K+ channels (IKCa) are involved in the I-R injury of the coronary microcirculation and that use of a new activator of the IKCa EBIO may protect the endothelium from hypoxia-reoxygenation (H-R) injury.
Methods Porcine coronary microarteries (diameter 200 ~ 450 μm) were subjected to hypoxia (PO2 < 5mmHg) for 30 min in Krebs at 37°C, or for 60 min in Krebs and St. Thomas cardioplegia (ST) with /without EBIO (600 μM) at 37°C or 4°C, followed by 30-min reoxygenation (n=8) in a myograph. Endothelium derived hyperpolarizing factor (EDHF)-mediated relaxation to bradykinin (−10 ~−6 logM) was studied in U46619-precontraction with inhibition of nitric oxide synthase and cyclooxygenase. The membrane potential (MP) and EDHF-mediated hyperpolarization in a single smooth muscle cell to bradykinin (−7 Log M) were measured by a microelectrode after 60-min hypoxia + 30-min reoxygenation with/without EBIO at 37°C (n=6).
Results & Conclusions Hypoxic exposure at 37°C decreased EDHF-mediated relaxation both in Krebs (30 min: 59.9±1.6 % vs. 81.2±3.5 %, p< 0.05; 60 min: 44.4± 6.0% vs. 82.7± 7.4%, p < 0.001) and ST (60 min: 28.9± 1.8% vs. 78.1± 3.0%, p < 0.001) and the reduction (p < 0.001) was also observed in 60-min hypothermic exposure (Krebs: 49.3± 3.0%; ST: 43.1±2.6%). The decrease in ST group was more significant at 37°C than at 4°C (p < 0.001). EBIO restored (p < 0.001) the relaxation at either 37°C (Krebs: 90.7±3.6%; ST: 82.6±2.6%) or 4°C (ST: 84.3±5.0%). Exposure to H-R decreased the EDHF-mediated hyperpolarization (6.0 ± 0.3 vs. 8.6 ± 0.5 mV, p < 0.05) that was recovered by the addition of EBIO (−7.8± 0.4 mv, p < 0.01). We therefore conclude that 1) H-R impairs IKCa -mediated mechanical activity and associated cellular electrophysiological properties with augmented impact of prolonged exposure; and 2) EBIO may prevent the H-R injury to the endothelium in coronary microcirculation even after prolonged H-R. Therefore, this study supports the use of IKCa activators as the new strategy during cardiac surgery.