Abstract
1. Left atrial and papillary muscle isolated from rat heart were suspended in a Magnus' apparatus and influenced by thiamine tetrahydrofurfuryldisulfide (TTFD) added to the medium at concentra tions of from 5×10-6 to 1.6×10-4g/ml.
2. Contractile tension of left atrial and papillary muscle driven by electrical stimulation was respectively increased by 27.2 and 55.0% of each control under the most effective conditions at 60 min after addition. Most of the drug effect remained even after the drug removal from medium.
3. The refractory period of these muscles estimated using the modified method of Govier was increased by the drug: the maximum increase in atrial muscle was 106.3% while that in papillary muscle was 38.3% of each control. Most of the drug effect on papillary muscle remained after the drug removal from medium while the effect on left atrial muscle reduced to the similar degree to that seen in the papillary muscle.
4. Maximum driving frequency of left atrial muscle estimated using the modified method of Tanz was decreased by the drug concentrations higher than 4×10-5g/ml and the drug effect remained after the drug removal from medium, while the drug effect on papillary muscle was slight at any drug concentration.
5. The drug thiamine used in place of TTFD little influenced the refractory period and the maximum driving frequency of these muscles at the drug concentrations of 10-6 and 2×10g/ml.
6. From the results, the effect of TTFD as an antiarrhythmic was discussed.
