Effects of simple indoles, noradrenaline, nicotine, and tyramine on action potential and contractility of the isolated guinea-pig papillary muscle

Abstract

1. Simultaneous recordings of both the transmembrane action potential and the contractions were made in isolated electrically driven papillary muscles of the guinea pig in order to compare the effects of 6-methoxyindole (6-MOI), 3-methylindole (3-MI) and 5-methylindole (5-MI) with those of noradrenaline (1.2 · 10⁻⁶ M), nicotine (2 · 10⁻⁵ M), and tyramine (5.8 · 10⁻⁶ M). 2. Noradrenaline, nicotine, tyramine and 6-MOI (5.4 · 10⁻⁴ M) enhanced the contractility whilst 3-MI (3.8 and 7.8 · 10⁻⁴ M) and 5-MI (1.9 and 3.8 · 10⁻⁴ M) had only irregular effects. The active compounds shortened the time-to-peak tension and increased the rate of relaxation. 3. The duration of the action potential was prolonged by noradrenaline, nicotine, and tyramine, but shortened by 3-MI, 5-MI, and 6-MOI. 4. The results showed that the effect of drugs on the action potential are not necessarily linked to those on contractility.