Halothane and isoflurane alter the Ca2+ binding properties of calmodulin

Area of Science:

• Biochemistry
• Neuroscience
• Pharmacology

Background:

• Calcium ions (Ca2+) are crucial for signal transduction and anesthesia.
• The direct impact of volatile anesthetics on Ca2+-binding proteins remains largely uncharacterized.
• This study investigates the effects of halothane and isoflurane on bovine brain calmodulin's Ca2+-binding properties.

Purpose of the Study:

• To determine how halothane and isoflurane influence the Ca2+-binding characteristics of calmodulin.
• To explore the dose-dependent effects of these volatile anesthetics on Ca2+ affinity.
• To identify potential interaction sites between anesthetics and calmodulin.

Main Methods:

• Calmodulin's intrinsic tyrosine fluorescence was measured across varying Ca2+ concentrations (10(-7)-10(-4)M).
• Experiments were conducted in the presence and absence of halothane and isoflurane under controlled conditions (pH 7.0, 37°C).
• Data were analyzed using the Hill equation and two-way ANOVA, with anesthetic concentrations verified by gas chromatography.

Main Results:

• Volatile anesthetics exhibited a dose-dependent effect on calmodulin's Ca2+-binding affinity.
• Low concentrations of halothane and isoflurane decreased Ca2+ affinity, while higher concentrations increased it.
• Anesthetic-induced shifts in Ca2+ binding were partially reversible at low concentrations but irreversible at high concentrations.

Conclusions:

• Halothane and isoflurane interact complexly with calmodulin, demonstrating a biphasic effect.
• Calmodulin's conformational changes upon Ca2+ binding may expose hydrophobic residues targeted by anesthetics.
• These findings suggest a novel mechanism for volatile anesthetic action involving direct interaction with Ca2+-binding proteins.