J Korean Med Sci.  2016 Apr;31(4):525-534. 10.3346/jkms.2016.31.4.525.

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

• Li B
• Pan Y
• Li X

• KMID: 2363690
• DOI: http://doi.org/10.3346/jkms.2016.31.4.525

Abstract

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.

Keyword

Diabetes Mellitus, Type 2; P-wave Duration; Sodium Current; Connexin-40; Connexin-43

MeSH Terms

Action Potentials
Animals
Blotting, Western
Connexin 43/metabolism
Connexins/metabolism
Diabetes Mellitus, Type 2/*physiopathology
Disease Models, Animal
Echocardiography
Electrocardiography
Fibrosis/pathology
Heart Atria/*diagnostic imaging/physiopathology
In Vitro Techniques
Male
Membrane Potentials
Microscopy, Fluorescence
Patch-Clamp Techniques
Potassium Channels/metabolism
Rats
Rats, Wistar
Connexin 43
Connexins
Potassium Channels

Figure

• 

  Fig. 1 Electrocardiographic and echocardiographic images from control and type 2 diabetic rats. (A) Abnormal prolongation of P-wave duration in diabetic rats (Lead II). (B) Left atrial anteroposterior diameter at end-diastole (LADd) in the parasternal long axis view. (C) Summary data of P-wave duration and LADd in control (N = 15) and T2DM (N = 20) rats. *P < 0.001 vs. control.

• 

  Fig. 2 Comparison of inward rectifier K+ current (Ik1) densities from atrial myocytes of normal and type 2 diabetic rats. (A) Ik1 traces from a normal atrial myocyte. (B) Ik1 traces from a diabetic atrial myocyte. (C) Ik1 density-voltage relationships in normal and diabetic rats. (D) Summary data of Ik1 densities (at -150 mv) in control (n = 11 cells from 3 rats) and diabetic (n = 11 cells from 3 rats) rats.

• 

  Fig. 3 Comparison of Na+ current (INa) densities from atrial myocytes of normal and type 2 diabetic rats. (A) INa traces from a normal atrial myocyte. (B) INa traces from a diabetic atrial myocyte. (C) INa density-voltage relationships in normal rats and type 2 diabetic rats. (D) Summary data of INa densities (at -30 mv) in control (n = 11 cells from 3 rats) and diabetic (n = 11 cells from 3 rats) rats.

• 

  Fig. 4 Recordings of action potentials in left atrial myocytes from control and type 2 diabetic rats. (A) Representative recordings of action potentials in left atrial myocytes from control (blue) and diabetic (red) rats. (B) Pooled data for APD at 50% (APD50) and 90% (APD90) repolarization in control (n = 11 cells from 3 rats) and diabetic rats (n = 11 cells from 3 rats) rats. (C) Summary data of resting membrane potential (RMP) in control (n = 11 cells from 3 rats) and diabetic (n = 11 cells from 3 rats) rats. (D) Summary data of action potential amplitude (APA) in control (n = 11 cells from 3 rats) and diabetic (n = 11 cells from 3 rats) rats. *P < 0.001 vs. control.

• 

  Fig. 5 Protein expression levels connexin-40 (Cx40) and connexin-43 (Cx43) in control and type 2 diabetic rats. (A) Representative Western blots for Cx40 protein in control and diabetic rats. (B) Representative Western blots for Cx43 protein in control and diabetic rats. (C) Relative ratios of Cx40/GAPDH and Cx43/GAPDH in control (n = 5) and diabetic (n = 5) rats. *P < 0.001 vs. control.

• 

  Fig. 6 Connexin-40 and connexin-43 protein immunostaining of left atrial tissue from a control and a type 2 diabetic rat. (A, B) Representative distribution of Cx40 (green) from control and diabetic rats, respectively; (C, D) Representative distribution of Cx43 (green) from control and diabetic rat, respectively. (A-D) α-actinin is stained red and nuclei are stained blue (Scale bars = 50 um).

• 

  Fig. 7 (A) Quantification of interstitial fibrosis by Masson’s trichrome staining of the left atrium from control and T2DM rats. (B) Quantification of %area fibrosis in control (n = 5) and T2DM (n = 7) rats. *P < 0.001 vs. control

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