Influence of halothane on calcium movements in isolated heart muscle and in isolated plasma membranes.

The influence of halothane on cellular calcium movements was studied in guinea-pig isolated atria and in isolated plasma membrane from guinea-pig myocardial muscle. In spontaneously beating atria halothane (1.6 X 10(-4) M) significantly reduced the rate of 45Ca-accumulation, but the total tissue calcium content and the exchangeable fractions remained unchanged. In isolated plasma membranes the rate of 45Ca- uptake was increased by halothane. Moreover, the binding capacity for calcium was increased as well upon exposure to halothane in concentrations that are sufficiently elevated to depress cardiac contractile force. This finding is interpreted in the sense of a reduced amount of ionized calcium that can be made available for excitation-contraction coupling, owing to the halothane- induced acceleration of calcium binding by plasma membranes. Kinetic experiments in isolated atria had already suggested that halothane probably acts at the level of the outward cell membrane. The changes in membraneous calcium migration may be causally related to the cardiodepressive influence of the anaesthetic agent.