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Background K+ currents and response to metabolic inhibition during early development in rat cardiocytes
G E Haddad1, E R Petrich, A P Zumino
1Department of Physiology, Faculty of Medicine, American University of Beirut, Lebanon.
Insights
Metabolic inhibition significantly shortens action potential duration in developing rat heart cells. The specific ionic currents affected depend on the cell
Area of Science:
- Cardiovascular Physiology
- Cellular Electrophysiology
- Developmental Biology
Background:
- Neonatal rat ventricle cells undergo significant electrophysiological changes during early development.
- Metabolic pathways, including oxidative phosphorylation and glycolysis, are crucial for cellular function.
- Understanding how metabolic inhibition affects cardiac electrophysiology is vital for developmental studies.
Purpose of the Study:
- To investigate the impact of metabolic inhibition on K+ background currents and action potential duration in developing rat ventricular cells.
- To characterize the specific ionic currents involved and their developmental regulation.
- To determine the influence of different metabolic inhibition strategies on electrophysiological properties.
Main Methods:
- Patch clamp technique (current and voltage clamp modes) was used on isolated neonatal rat ventricle cells (1 and 7 days old).
- Action potentials and ionic currents were measured under control conditions and following metabolic inhibition.
- Metabolic inhibition was achieved using 2,4-dinitrophenol (2,4-DNP) for oxidative phosphorylation and 2-deoxyglucose (2-DG) for glycolysis.
Main Results:
- Action potential duration shortened by approximately 50% upon metabolic inhibition in 1-day-old rats.
- Developmental changes included cell surface increase, membrane hyperpolarization, and action potential shortening.
- Specific K+ background currents (inwardly rectifying, glibenclamide-sensitive, and leak components) were identified and their properties varied with age and metabolic inhibition.
Conclusions:
- The electrophysiologic response to metabolic inhibition in developing cardiac cells is dependent on the cell's developmental stage.
- The relative contribution of oxidative phosphorylation and glycolysis influences the observed electrophysiological changes.
- Specific ion channel activities are modulated by metabolic status during cardiac development.
Abstract:
The effects of metabolic inhibition on K+ background currents and action potential duration were investigated in neonatal rat ventricle cells during early development. Action potentials and ionic currents were measured with the patch clamp technique in current and voltage clamp mode in cells isolated with collagenase from 1 day and 7 day old rats. During the first postnatal week, the cell surface increased from 1700 to 2210 microm2 and the membrane hyperpolarized from -66.1 to -72.0 mV. Concomitantly the action potential shortened and the plateau became more negative. Inhibition of oxidative phosphorylation (50 microM 2,4 DNP) or of glycolysis in 1 day old rats (5 mM 2-deoxyglucose, 2-DG) also shortened the action potential by about 50% after 5 min exposure. The background current measured in the absence of INa, ICa,L, and Ito included: (1) an inward rectifying component whose I/V curves crossed over when measured in 6, 15, or 30 mM [K]o and showed an increase in slope conductance when [K]o was raised. Inward rectification was abolished by 2.4 mM Ba2+ in 1 day old cells and by 0.2 mM one week after birth; (2) a glibenclamide (100 microM) sensitive component that developed with time after membrane rupture (5-10 min) showing a higher current density in 7 than in 1 day old animals (1.4 vs 0.2 microA x cm-2 at -50 mV); and (3) a small and almost linear leak component of comparable amplitude in both age groups. Inhibition of oxidative phosphorylation with 2.5 microM carbonylcyanide m-chlorophenylhydrazone induced the development of background currents with different properties in both age groups: An inwardly rectifying Ba2+ sensitive current in 1 day old cells and a glibenclamide sensitive outwardly rectifying current in the 7 day old group. In contrast, exposure to 5 mM 2-DG provoked in all cells the development of an outwardly rectifying current that was blocked by glibenclamide. We conclude that the electrophysiologic response to metabolic inhibition is determined by the relative importance of the metabolic pathways present which in turn depends on the developmental state of the cells.