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Stereoselective effects of the enantiomers of bupivacaine on the electrophysiological properties of the guinea‐pig papillary muscle

1991; Wiley; Volume: 103; Issue: 1 Linguagem: Inglês

10.1111/j.1476-5381.1991.tb12336.x

1476-5381

Filip Vanhoutte, Johan Vereecke, Norbert Verbeke, Edward Carmeliet,

Advanced MRI Techniques and Applications

Direct myocardial effects of the S (−)‐ and R (+)‐enantiomers of bupivacaine were compared in the guinea‐pig isolated papillary muscle by recording transmembrane action potentials with the standard microelectrode technique. In 5.4 m m K + , at a stimulation rate of 1 Hz, the maximal rate of depolarization () was reduced to 59.9 ± 1.4% ( n = 10) of control (mean ± s.e.mean) in the presence of 10 μ m R (+)‐bupivacaine, and to 76.7 ± 1.2% ( n = 14) in the presence of the same concentration of S (−)‐bupivacaine. This was mainly due to a difference in time constant at which block dissipated during the diastolic period. Recovery was slower in the presence of R (+)‐bupivacaine. The slower recovery in the presence of R (+)‐bupivacaine resulted also in a more pronounced frequency‐dependent block of . Time constants for recovery from use‐dependent block became significantly faster for both enantiomers on hyperpolarization, while no significant change was observed at depolarization. At all membrane potentials recovery was slower in the presence of R (+)‐bupivacaine. The action potential duration (APD) was shortened to a greater extent in the presence of R (+)‐bupivacaine over a large range of stimulation frequencies. We conclude that S (−)‐bupivacaine affects and APD in the guinea‐pig papillary muscle less than the R (+)‐enantiomer at different rates of stimulation and resting membrane potentials.