Bursting electrical activity generated in the presence of KATP channel blockers. Pharmacology, sensitivity to intracellular pH and modulation by glucose metabolism

Increase of ATP-sensitive potassium (K(ATP)) channels in the heart of type-1 diabetic rats

Background

An impairment of cardiovascular function in streptozotocin (STZ)-diabetic rats has been mentioned within 5 days-to-3 months of induction. ATP-sensitive potassium (K_ATP) channels are expressed on cardiac sarcolemmal membranes. It is highly responsive to metabolic fluctuations and can have effects on cardiac contractility. The present study attempted to clarify the changes of cardiac K_ATP channels in diabetic disorders.

Methods

Streptozotocin-induced diabetic rats and neonatal rat cardiomyocytes treated with a high concentration of glucose (a D-glucose concentration of 30 mM was used and cells were cultured for 24 hr) were used to examine the effect of hyperglycemia on cardiac function and the expression of K_ATP channels. K_ATP channels expression was found to be linked to cardiac tonic dysfunction, and we evaluated the expression levels of K_ATP channels by Western blot and Northern blot analysis.

Results

The result shows diazoxide produced a marked reduction of heart rate in control group. Furthermore, the methods of Northern blotting and Western blotting were employed to identify the gene expression of K_ATP channel. Two subunits of cardiac K_ATP channel (SUR2A and kir 6.2) were purchased as indicators and showed significantly decreased in both diabetic rats and high glucose treated rat cardiac myocytes. Correction of hyperglycemia by insulin or phlorizin restored the gene expression of cardiac K_ATP in these diabetic rats.

Conclusions

Both mRNA and protein expression of cardiac K_ATP channels are decreased in diabetic rats induced by STZ for 8 weeks. This phenomenon leads to result in desensitization of some K_ATP channel drugs.