Malignant hyperthermia: effects of halothane on the surface membrane

Area of Science:

• Muscle physiology
• Anesthesiology
• Pharmacology

Background:

• Malignant hyperthermia is a severe pharmacogenetic disorder of skeletal muscle.
• Anesthetic agents like halothane can trigger malignant hyperthermia episodes in susceptible individuals.
• Understanding the cellular mechanisms of halothane sensitivity is crucial for patient safety.

Purpose of the Study:

• To investigate the electrical properties of normal and malignant hyperthermia-susceptible (MHS) muscle fibers.
• To determine the effects of halothane on these electrical properties.
• To elucidate the role of membrane potential and action potentials in halothane-induced contractures.

Main Methods:

• Intact muscle fibers from normal and MHS pigs were studied.
• Resting membrane potentials, action potentials, and current-voltage relationships were measured.
• Experiments were conducted with and without varying concentrations of halothane, with some fibers preincubated with dantrolene.

Main Results:

• No significant differences in resting potentials or membrane conductances were found between normal and MHS fibers.
• Halothane induced contractures in MHS muscle at concentrations ≥0.8%, independent of membrane depolarization.
• Halothane significantly altered action potential shapes more profoundly and at lower concentrations in MHS fibers compared to normal fibers; dantrolene partially prevented these changes.

Conclusions:

• Halothane-induced contractures in MHS muscle are not directly caused by surface membrane depolarization.
• MHS muscle fibers exhibit heightened sensitivity to halothane's effects on action potentials.
• Dantrolene demonstrates a protective effect against halothane-induced alterations in MHS muscle action potentials.