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259 Glibenclamide attenuates post-repolarization refractoriness in engineered heart tissue model
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Canadian Journal of Cardiology Volume 27 2011
259 GLIBENCLAMIDE ATTENUATES POST-REPOLARIZATION REFRACTORINESS IN ENGINEERED HEART TISSUE MODEL TA Farid, S Massé, K Nair, O Khan, J Jacob, M Kusha, PF Lai, N Thavandiran, M Radisic, K Nanthakumar Toronto, Ontario
Though the effect of glibenclamide on short duration ischemia and refractoriness has been studied, it’s effect on long duration ischemia and post-repolarization refractoriness has not been investigated. The purpose of this study was to investigate the effect of KATP channel blockage, using libenclamide, on post-repolarization refractoriness secondary to long duration ischemia. METHODS/RESULTS: Neonatal rat (Sprague-Dawley) and mouse [YFP transgenic, 129-Tg(CAG-EYFP)7AC5Nagy/J; Jackson Laboratory] hearts were harvested and enzymatically digested using trypsin (6120 U/mL, 4 °C, 5-8 h), followed by series of collagenase digestion steps. Cardiomyocytes (CM) were seeded onto the collagen scaffold and cultivated in the environmental chamber with electrical stimulation to create engineered tissue construct (ETC) model. ETCs were paced, locally using 2 30-gauge silver wires applied to one end. A base pace train (S1) of 1000 ms was used. An extra-stimulus (S2) was delivered starting at 900ms. The duration of S2 was decreased in 50 ms increments until loss of capture was achieved. The S2 was then increased by 100ms and decreased by 10 ms intervals until capture was lost. The data was recorded from 12 CMs in the control condition. After recording in control conditions, 7 CMs were incubated for 15 minutes with ⬙ischemic Tyrode’s solution⬙ (no glucose, bubbled with nitrogen for 30-45 minutes) [ischemic group] and 5 CMs were incubated with ischemic tyrode’s solution plus 10 M Glibenclamide [treatment group]. Repeated measure ANOVA was employed to analyze the data and a P ⬍ 0.05 was considered statistically significant. Mean effective refractory period (ERP) was 346 ⫾ 17 ms, 673 ⫾ 51 ms and 498 ⫾ 44 ms in the control, ischemia and treatment groups respectively. The difference between control and ischemia groups was statistically significant (P ⫽ 0.012) while the difference between control and treatment groups was not statistically significant (P ⫽ 0.1) (Figure 1). CONCLUSION: Glibenclamide attenuates post-repolarization refractoriness in an ischemic engineered tissue model. The exact mechanism by which this attenuation occurs is yet to be elucidated. BACKGROUND:
260 A NOVEL MISSENSE SCN5A GENE MUTATION CAUSING LQT3 IN A LARGE FIRST NATIONS FAMILY MJ Gardner, J Marcadier, A Crowley, J Hathaway, A Warren, S Dyack Halifax, Nova Scotia BACKGROUND: Long QT 3 syndrome is due to SCN5A sodium channel gene mutations. We detected a novel possibly deleterious SCN5A gene mutation (2192C⬎T) in a young girl following a diagnosis of LQT syndrome. To determine if this mutation was disease causing, we performed genetic mutation and ECG analysis in consenting family members. METHODS: We invited family members to attend clinics held in their first nations community. All subjects underwent a history, physical exam, 12 lead ECG and had blood samples collected for mutation analysis. One hundred and fifty five family members participated. All were assessed by an adult or pediatric cardiologist and genetic counselors over a two year period. There were 86 females and 69 males ranging in age from 1 to 82 years (mean 36 years). The QT interval was measured manually using calipers by one of us (MG) without knowledge of the genetic test results. The QTc was calculated using Bazett’s formula. The QTc values between the gene positive (gene⫹) and gene negative (gene-) groups were compared using Student’s t-test. RESULTS: There was no difference in age or gender distribution between the gene⫹ and gene- groups. The mean QTc for the gene⫹ group was 461⫹/⫺ 21 ms versus 419⫹/⫺ 22 ms for the gene- group (P ⬍ .001). The figure displays the QTc values in 20 ms increments for each group. CONCLUSION: This novel SCN5A sodium channel gene mutation results in a significant prolongation of the QTc and is thus
Canadian Journal of Cardiology Volume 27 2011
259 GLIBENCLAMIDE ATTENUATES POST-REPOLARIZATION REFRACTORINESS IN ENGINEERED HEART TISSUE MODEL TA Farid, S Massé, K Nair, O Khan, J Jacob, M Kusha, PF Lai, N Thavandiran, M Radisic, K Nanthakumar Toronto, Ontario
Though the effect of glibenclamide on short duration ischemia and refractoriness has been studied, it’s effect on long duration ischemia and post-repolarization refractoriness has not been investigated. The purpose of this study was to investigate the effect of KATP channel blockage, using libenclamide, on post-repolarization refractoriness secondary to long duration ischemia. METHODS/RESULTS: Neonatal rat (Sprague-Dawley) and mouse [YFP transgenic, 129-Tg(CAG-EYFP)7AC5Nagy/J; Jackson Laboratory] hearts were harvested and enzymatically digested using trypsin (6120 U/mL, 4 °C, 5-8 h), followed by series of collagenase digestion steps. Cardiomyocytes (CM) were seeded onto the collagen scaffold and cultivated in the environmental chamber with electrical stimulation to create engineered tissue construct (ETC) model. ETCs were paced, locally using 2 30-gauge silver wires applied to one end. A base pace train (S1) of 1000 ms was used. An extra-stimulus (S2) was delivered starting at 900ms. The duration of S2 was decreased in 50 ms increments until loss of capture was achieved. The S2 was then increased by 100ms and decreased by 10 ms intervals until capture was lost. The data was recorded from 12 CMs in the control condition. After recording in control conditions, 7 CMs were incubated for 15 minutes with ⬙ischemic Tyrode’s solution⬙ (no glucose, bubbled with nitrogen for 30-45 minutes) [ischemic group] and 5 CMs were incubated with ischemic tyrode’s solution plus 10 M Glibenclamide [treatment group]. Repeated measure ANOVA was employed to analyze the data and a P ⬍ 0.05 was considered statistically significant. Mean effective refractory period (ERP) was 346 ⫾ 17 ms, 673 ⫾ 51 ms and 498 ⫾ 44 ms in the control, ischemia and treatment groups respectively. The difference between control and ischemia groups was statistically significant (P ⫽ 0.012) while the difference between control and treatment groups was not statistically significant (P ⫽ 0.1) (Figure 1). CONCLUSION: Glibenclamide attenuates post-repolarization refractoriness in an ischemic engineered tissue model. The exact mechanism by which this attenuation occurs is yet to be elucidated. BACKGROUND:
260 A NOVEL MISSENSE SCN5A GENE MUTATION CAUSING LQT3 IN A LARGE FIRST NATIONS FAMILY MJ Gardner, J Marcadier, A Crowley, J Hathaway, A Warren, S Dyack Halifax, Nova Scotia BACKGROUND: Long QT 3 syndrome is due to SCN5A sodium channel gene mutations. We detected a novel possibly deleterious SCN5A gene mutation (2192C⬎T) in a young girl following a diagnosis of LQT syndrome. To determine if this mutation was disease causing, we performed genetic mutation and ECG analysis in consenting family members. METHODS: We invited family members to attend clinics held in their first nations community. All subjects underwent a history, physical exam, 12 lead ECG and had blood samples collected for mutation analysis. One hundred and fifty five family members participated. All were assessed by an adult or pediatric cardiologist and genetic counselors over a two year period. There were 86 females and 69 males ranging in age from 1 to 82 years (mean 36 years). The QT interval was measured manually using calipers by one of us (MG) without knowledge of the genetic test results. The QTc was calculated using Bazett’s formula. The QTc values between the gene positive (gene⫹) and gene negative (gene-) groups were compared using Student’s t-test. RESULTS: There was no difference in age or gender distribution between the gene⫹ and gene- groups. The mean QTc for the gene⫹ group was 461⫹/⫺ 21 ms versus 419⫹/⫺ 22 ms for the gene- group (P ⬍ .001). The figure displays the QTc values in 20 ms increments for each group. CONCLUSION: This novel SCN5A sodium channel gene mutation results in a significant prolongation of the QTc and is thus