Abstract
Effects of externally applied noradrenaline and isoprenaline on the electrical and mechanical activities of the guinea-pig was deferens were observed using the double sucrose gap method.
1. Noradrenaline (10-8-10-5g/ml) depolarized the membrane, reduced the membrane resistance, produced spike generation and brought about contraction (α-response). These effects were suppressed by treatment with phentolamine (10-6-10-5g/ml).
2. The α-response is caused by increased Na and K conductances, and probably by increased Ca conductance also. The Cl ion reduced the α-response due to high conductance of the membrane.
3. Isoprenaline (10-7-10-8g/ml) neither depolarized the membrane nor changed the membrane resistance but reduced the amplitude of the phasic contraction (β-response) evoked by an outward current pulse. The suppression of the contraction was blocked by treatment with propranolol (10-6g/ml).
4. Ouabain (10-6g/ml) depolarized the membrane, reduced the membrane resistance and increased the spike frequency. Under the above conditions, effects of catecholamines were not suppressed.
5. The relationships between the membrane potential and tension development were observed using the microelectrode and double sucrose gap methods. The amplitudes of the phasic response of the contracture were closely related to membrane potential levels displaced by excess K ion, but the amplitudes of the tonic response were not related.
6. In excess K-Krebs solution (below 59mM), noradrenaline (10-7-10-6g/ml) and isoprenaline (10-7-10-6g/ml) were similar to those observed in 5.9mM K-Krebs. When external Na ion was removed, however, the effects of noradrenaline and isoprenaline were absent.
7. If K-Krebs solution was in excess (above 59mM), the amplitude of the tonic response of the contracture was less than 20% of the amplitude of the phasic response. Noradrenaline (10-8-10-9g/ml) and isoprenaline (10-6-10-5g/ml) did not have any marked effect on electrical and mechanical properties of the muscle.
8. Acetylcholine (10-7-10-6g/ml) had effects similar to those of noradrenaline on the normal and depolarized muscle.
9. Possible actions of noradrenaline and isoprenaline in the normal and depolarized muscles were discussed in relation to the electrical and mechanical properties of the guinea-pig taenia coli.
