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EFFECTS OF MEXILETINE ON TRANSMEMBRANE ACTION POTENTIALS AS AFFECTED BY EXTERNAL POTASSIUM CONCENTRATION AND BY RATE OF STIMULATION IN GUINEA‐PIG PAPILLARY MUSCLES
Author(s) -
Sada Hideaki,
Ban Takashi,
Oshita Shuzo
Publication year - 1980
Publication title -
clinical and experimental pharmacology and physiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.752
H-Index - 103
eISSN - 1440-1681
pISSN - 0305-1870
DOI - 10.1111/j.1440-1681.1980.tb00116.x
Subject(s) - mexiletine , chemistry , quinidine , repolarization , stimulation , potassium , refractory period , effective refractory period , medicine , endocrinology , guinea pig , pharmacology , electrophysiology , organic chemistry
SUMMARY 1. The effects of mexiletine and quinidine were compared on transmembrane potentials in guinea‐pig papillary muscles, using conventional microelectrode techniques. 2. Mexiletine (23–1 μ mol/1) decreased the maximum rate of rise of the action potential (V̇max) and increased the ratio of the effective refractory period to the action potential duration at 90% repolarization level (ERP/APD90); these effects were prominent with elevation of the external potassium concentration ([K] o ) from 2–7 to 5–4, 81 and 100mmol/1. 3. The percentage decrease in V̇max induced by 5 and 10 μmol/1 of quinidine was approximately constant in 2–7, 5–4 and 100 mmol/1 [K] o solutions. 4. The decrease in V̇max produced by mexiletine was progressively increased as the driving rate was raised from 0–25 to 5H z. This rate‐dependent change was pronounced when the concentration was raised from 23–1 to 46–2 and 92–4 /μmol/1. 5. Mexiletine in concentrations of 23–1 and 92–4 μ miol/1 delayed the recovery of V̇max in a premature action potential to the level of V̇max in the conditioning action potentials at the driving rate of 0–25 Hz. 6. It appears that mexiletine exerts its anti‐arrhythmic action by a selective depressant effect on depolarized cells (high [K] o ) and cells with high frequency discharges, as is the case with lignocaine.