Tetraethylammonium-Sensitive ventricular repolarization in diabetic rat myocardium: effects of rosiglitazone.

Figures

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  Figure 1. Experimental setup for intracellular electrophysiological recording. Schematic illustration of the experimental setup for intracellular recordings in isolated rat ventricular papillary muscles. Preparations were continuously superfused with oxygenated Krebs-Henseleit solution and electrically stimulated throughout the experiment. Transmembrane action potentials were digitized and analyzed using a computer-based acquisition system.

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  Figure 2. Effects of rosiglitazone on body weight in streptozotocin-induced diabetic rats. Weekly body weight is expressed as a percentage of baseline, over the 8-week experimental period. Control animals showed progressive weight gain, while diabetic rats exhibited impaired weight gain and progressive weight loss. Rosiglitazone treatment partially attenuated diabetes-associated weight reduction. Data are presented as mean ± standard error of the mean.

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  Figure 3. Blood glucose levels during the experimental period. Weekly fasting blood glucose concentrations measured over the 8-week experimental period. Streptozotocin caused persistent hyperglycemia in diabetic animals. Rosiglitazone significantly reduced blood glucose concentrations but did not normalize glycemic status. Data are presented as mean ± standard error of the mean.

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  Figure 4. Effects of tetraethylammonium and rosiglitazone on resting membrane potential. Resting membrane potential recorded from isolated ventricular papillary muscles from control and diabetic rats before and after tetraethylammonium administration. Diabetes caused membrane depolarization, while rosiglitazone partially restored resting membrane potential toward control values. Tetraethylammonium altered membrane polarization in both control and diabetic myocardium. Data are presented as mean ± standard error of the mean.

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  Figure 5. Effects of tetraethylammonium and rosiglitazone on action potential amplitude. Action potential amplitude recorded from isolated ventricular papillary muscles from control and diabetic rats before and after tetraethylammonium administration. Diabetes reduced myocardial excitability, while rosiglitazone partially improved action potential amplitude. Tetraethylammonium altered electrophysiological responses, highlighting the contribution of potassium conductances to action potential generation. Data are presented as mean ± standard error of the mean.

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  Figure 6. Effect of tetraethylammonium on half-repolarization time. Half-repolarization time (½RT) in isolated ventricular papillary muscles before and after tetraethylammonium (TEA; 2 mmol/L). Mean ½RT changed from 18 to 38 ms in C (+20 ms), 29 to 46 ms in C+RSG (+17 ms), 60 to 65 ms in D (+5 ms), and 55 to 69 ms in D+RSG (+14 ms). Diabetic myocardium had longer baseline and post-TEA values, but the absolute increment in untreated diabetes was smaller than in untreated controls. TEA is non-selective; the figure does not identify a specific current or channel subtype. Inferential comparisons must be based on the revised group × TEA repeated-measures model.