Troglitazone but not pioglitazone affects ATP-sensitive K(+) channel activity

Area of Science:

• Pharmacology
• Cellular Physiology
• Molecular Biology

Background:

• Thiazolidinediones are used to treat type 2 diabetes.
• ATP-sensitive potassium (K(ATP)) channels play crucial roles in cellular functions, including insulin secretion and cardiac activity.
• Understanding the molecular mechanisms of thiazolidinedione action is important for drug development.

Purpose of the Study:

• To compare the effects of troglitazone and pioglitazone on pancreatic beta-cell and cardiac K(ATP) channel activities.
• To investigate the potential of these drugs to modulate cellular functions through K(ATP) channel activity.

Main Methods:

• Heterologous expression of sulfonylurea receptor 1 (SUR1) plus Kir6.2 and sulfonylurea receptor 2A (SUR2A) plus Kir6.2 in COS-1 cells to reconstitute pancreatic and cardiac K(ATP) channels.
• Measurement of [86Rb(+)] efflux in the presence of metabolic inhibitors to assess channel activity.
• Confirmation of results using electrophysiological techniques.
• Assessment of the effects of channel openers diazoxide and pinacidil on K(ATP) channel activity in the presence of troglitazone.

Main Results:

• Troglitazone significantly inhibited [86Rb(+)] efflux in both pancreatic and cardiac K(ATP) channel types.
• The inhibitory effect of troglitazone on K(ATP) channels was confirmed by electrophysiological studies.
• Troglitazone abolished the increase in [86Rb(+)] efflux induced by channel openers diazoxide and pinacidil.
• Pioglitazone did not exhibit any significant effect on the activity of either pancreatic or cardiac K(ATP) channels.

Conclusions:

• Troglitazone modulates cellular functions, potentially including insulin secretion, through the inhibition of K(ATP) channels.
• Pioglitazone does not appear to affect K(ATP) channel activity.
• These findings highlight differential mechanisms of action between troglitazone and pioglitazone concerning K(ATP) channels.