Type 2 Diabetes Induces Prolonged P-wave Duration without Left Atrial Enlargement

Prolonged P-wave duration has been observed in diabetes. However, the underlying mechanisms remain unclear. The aim of this study was to elucidate the possible mechanisms. A rat model of type 2 diabetes mellitus (T2DM) was used. P-wave durations were obtained using surface electrocardiography and sizes of the left atrium were determined using echocardiography. Cardiac inward rectifier K+ currents (I(k1)), Na+ currents (I(Na)), and action potentials were recorded from isolated left atrial myocytes using patch clamp techniques. Left atrial tissue specimens were analyzed for total connexin-40 (Cx40) and connexin-43 (Cx43) expression levels on western-blots. Specimens were also analyzed for Cx40 and Cx43 distribution and interstitial fibrosis by immunofluorescent and Masson trichrome staining, respectively. The mean P-wave duration was longer in T2DM rats than in controls; however, the mean left atrial sizes of each group of rats were similar. The densities of I(k1) and I(Na) were unchanged in T2DM rats compared to controls. The action potential duration was longer in T2DM rats, but there was no significant difference in resting membrane potential or action potential amplitude compared to controls. The expression level of Cx40 protein was significantly lower, but Cx43 was unaltered in T2DM rats. However, immunofluorescent labeling of Cx43 showed a significantly enhanced lateralization. Staining showed interstitial fibrosis was greater in T2DM atrial tissue. Prolonged P-wave duration is not dependent on the left atrial size in rats with T2DM. Dysregulation of Cx40 and Cx43 protein expression, as well as fibrosis, might partly account for the prolongation of P-wave duration in T2DM.

A Modified Method for Acute Isolation of Atrial Myocytes in Diabetic Rats / 中国医科大学学报

Objective To establish a stable method for acute isolation of atrial myocytes in diabetic rats,so as to provide materials for electrophysio?logical study of diabetic rats. Methods Streptozotocin(STZ)was used to establish type I diabetic model. Atrial myocytes were isolated with modi?fied perfusion buffer by Langendorff perfusion. The atrial myocytes were morphologically observed with optical microscope and identified by morphol?ogy and immunofluorescence staining. The action potential was recorded by patch clamp technique. Results STZ can establish a stable type I dia?betic model. The modified perfusion method can yield calcium tolerant and spindle shaped atrial myocytes. Immunofluorescence indicated that atrial myocytes were positive for Kv1.5 which was expressed in atrial myocytes. The atrial myocytes obtained by this method were able to generate action po?tentials. Conclusion The modified perfusion method is suitable for acute isolation of atrial myocytes in rats with diabetes mellitus,which may help to study the electrophysiology of diabetic heart.