Sex differences in connexin-43 expression in left ventricles of aging rats

Cardiac gap junctions have been implicated in maintaining intercellular electrical and metabolic couplings. The abnormalities in connexin-43 (Cx43) lead to conduction defects and contractile dysfunction. We have evaluatedthe expression and phoshorylation status of Cx43 in the left ventricular myocardium of male and female 16-month-old rats submitted to 14-week L-thyroxine (T4) treatment. Western blot analysis revealed the presence of fully or intermediately phosphorylated and unphosphorylated forms of Cx43. We have found no significant differences in Cx43 expression and phosphorylation between T4-treated and control untreated animals. However, expression of Cx43 was significantly higher in female compared to male rats. We conclude that T4 administration has no effect on Cx43 expression, but there are sex-dependent differences in Cx43 expression in the left ventricles between aging male and female rats

Autoantibodies against G-Protein-Coupled Receptors Modulate Heart Mast Cells

Mast cells are believed to be involved in myocardial tissue remodelling under pathophysiological conditions. We examined the effects of autoantibodies against G-protein-coupled receptors in sera of patients with heart diseases on myocardial mast cells in the cultured neonatal Sprague-Dawley rat heart cells. Cells collected at day 3 and 10 of the culture were preincubated with autoantibodies against alpha1-adrenoceptor and angiotensin II AT1-receptor, agonist phenylephrine and angiotensin II, and control IgG. The pretreated cultured cells were stained for selected mast cell markers tryptase, chymase and TNF-alpha. The cultured cells were also processed for observation with electron microscopy. The autoantibodies-treatment of the 3-day cultured cells caused both increased intensity of immunofluorescence (p < 0.05) and their enlarged diameters of the mast cells when compared to age-matched ones. In contrast, the fluorescence of preincubated 10-day-old mast cells was decreased compared with controls (p < 0.01). In control samples, the fluorescence of 10-day-old mast cells was significantly higher than that of 3-day-old ones (p &lt; 0.001). Results of electron microscopy examination demonstrated there was an increased granulation of treated 3-day-old mast cells, while a degranulation of mast cells at day 10 of application. The results suggest the modulation effect of the autoantibodies against G-protein-coupled receptors on mast cells, indicating a potential functional link between the autoantibodies against G-protein-coupled receptors and the mast cells in progression of heart disease

Propagation of the cardiac impulse in the diabetic rat heart: reduced conduction reserve

Diabetes mellitus is a growing epidemic with severe cardiovascular complications. Although much is known about mechanical and electrical cardiac dysfunction in diabetes, few studies have investigated propagation of the electrical signal in the diabetic heart and the associated changes in intercellular gap junctions. This study was designed to investigate these issues, using hearts from control and diabetic rats. Diabetic conditions were induced by streptozotocin (STZ), given i.v. 7–14 days before experiments. Optical mapping with the voltage-sensitive dye di-4-ANEPPS, using hearts perfused on a Langendorff apparatus, showed little change in baseline conduction velocity in diabetic hearts, reflecting the large reserve of function. However, both the gap junction uncoupler heptanol (0.5–1 mm) and elevated potassium (9 mm, to reduce cell excitability) produced a significantly greater slowing of impulse propagation in diabetic hearts than in controls. The maximal action potential upstroke velocity (an index of the sodium current) and resting potential was similar in single ventricular myocytes from control and diabetic rats, suggesting similar electrical excitability. Immunoblotting of connexin 43 (Cx43), a major gap junction component, showed no change in total expression. However, immunofluorescence labelling of Cx43 showed a significant redistribution, apparent as enhanced Cx43 lateralization. This was quantified and found to be significantly larger than in control myocytes. Labelling of two other gap junction proteins, N-cadherin and β-catenin, showed a (partial) loss of co-localization with Cx43, indicating that enhancement of lateralized Cx43 is associated with non-functional gap junctions. In conclusion, conduction reserve is smaller in the diabetic heart, priming it for impaired conduction upon further challenges. This can desynchronize contraction and contribute to arrhythmogenesis