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Conformational state-dependent effects of halothane on cardiac Na+ current
H U Weigt1, G C Rehmert, Z J Bosnjak
1Medical College of Wisconsin, Milwaukee 53226, USA.
Anesthesiology
|January 7, 1998
Summary
Halothane significantly depresses cardiac sodium current (I(Na)) in a voltage-dependent manner, with effects amplified when channels are inactivated. This indicates a complex interaction between halothane and sodium channel states.
Area of Science:
- Cardiovascular Pharmacology
- Ion Channel Physiology
- Anesthetic Mechanisms
Background:
- Cardiac sodium channels (Na+) are voltage-gated, existing in closed, open, and inactivated states.
- Halothane is an anesthetic agent with known effects on ion channels.
Purpose of the Study:
- To investigate the voltage-dependent effects of halothane on cardiac sodium current (I(Na)).
- To characterize the state-dependent interaction of halothane with cardiac Na+ channels.
Main Methods:
- Whole-cell patch-clamp technique in isolated guinea pig ventricular myocytes.
- I(Na) recorded at various holding potentials (V(H)) (-110, -80, -65 mV).
- State-dependent block assessed via frequency dependence, tonic block, and veratridine-induced removal of inactivation.
Main Results:
- Halothane caused V(H)-dependent depression of peak I(Na), increasing from 24.4% at -110 mV to 75.2% at -65 mV.
- Halothane slowed recovery from inactivation at -80 mV and exhibited use-dependent block at this potential.
- Veratridine-induced removal of inactivation abolished V(H) dependence, but current depression persisted.
Conclusions:
- Halothane's depressant effect on cardiac I(Na) is state-dependent, potentiated by channel inactivation.
- Complex interactions exist between halothane and different conformational states of the Na+ channel.
- These findings elucidate halothane's impact on cardiac electrophysiology via Na+ channel modulation.