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Effects of (+)- and (±)-sotalol on repolarizing outward currents and pacemaker current in sheep cardiac Purkinje fibres

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Summary

This study was aimed to differentiate the action of (+)- and (±)-sotalol (10–1000 μmol/l) on membrane currents which are active during the repolarization of cardiac action potentials Effects where studied in shortened sheep cardiac Purkinje fibres with the two-microelectrode voltage-clamp technique Action potentials were activated at a frequency of 0.25 Hz and membrane currents at 0.03 Hz or 0.05 Hz in most experiments.

Out of the currents investigated the transient outward current (ito) reacted most sensitively to (+)- and (±)-sotalol. Ito-amplitude was decreased on the average to 77% of reference at 10 μmol/l and to 53% at 1000 μmol/l (+)- or (±)-sotalol. The maximally available ito-current was decreased but the voltage-dependent control of inactivation was left nearly unchanged. The initial inwardly rectifying current (iKi), which propels the last repolarization phase of the action potential and controls resting potential to a large extent was reduced on the average to 93% of reference at 10 μmol/l and to 62% at 1000 μmol/l (+)- or (±)-sotalol. Time-dependent (delayed) outward current (iK) was on the average not affected by (+)- or (±)-sotalol up to 100 μmol/l and was decreased to 84% of reference current under the influence of 1000 μmol/l. An initial outward current, which is activated at positive membrane potentials (iinst) was not clearly affected by (+)- or (±)-sotalol at concentrations up to 1000 μmol/l Pacemaker current (if) was not influenced by the drugs up to 100 μmol/l. Only at 1000 μmol/l was the amount of available if-current decreased to 79% of reference. (The potential-dependent control of activation was not affected) Time constants of time-dependent currents ito, iK and if did not change in concentrations up to 1000 μmol/l of the drug.

Action potential duration increased at (+)- or (±)-sotalol concentrations ≥ 10 μmol/l and maximal prolongation was achieved at concentrations of 100–300 μmol/l Resting potential remained nearly unchanged at these concentrations, but the membranes depolarized at 1000 μmol/l. According to our data action potential prolongation in sheep Purkinje fibres under the influence of (+)- and (±)-sotalol correlates to the drug-induced block to ito-current and inwardly rectifying iK1-current.

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Authors and Affiliations

  1. Institut für Pharmakologie der Universität Düsseldorf, Moorenstrasse 5, D-4000, Düsseldorf, Germany

    F. Berger, U. Borchard & D. Hafner

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  1. F. Berger
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  2. U. Borchard
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  3. D. Hafner
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Supported by the Deutsche Forschungsgemeinschaft SFB 242, C 1

Send offprint requests to U. Borchard at the above address

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Berger, F., Borchard, U. & Hafner, D. Effects of (+)- and (±)-sotalol on repolarizing outward currents and pacemaker current in sheep cardiac Purkinje fibres. Naunyn-Schmiedeberg's Arch. Pharmacol. 340, 696–704 (1989). https://doi.org/10.1007/BF00717747

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  • DOI: https://doi.org/10.1007/BF00717747

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