Effects of tetrandrine on isoprenaline and calcium-mediated positive chronotropic action in isolated rabbit atria
Abstract
In isolated spontaneously beating atria of rabbits, tetrandrine (Tet) and verapamil (Ver) shifted the concentration-rate curves to isoprenaline (Iso) to the right in a non-parallel manner and depressed their maxima. (±)-propranolol behaved as a competitive β-adrenoceptor antagonist.
The pD’ values of Tet and Ver were 6.48±0.45 and 4.30±0.18, respectively. Hence the antagonistic effect of Ver was stronger than that of Tet. The pA of propranolol=7.86+0.21.
Tet and Ver antagonized the positive chronotropic responses to Ca (3.3 mM) in spontaneously beating rabbit atria.
It is proposed that Tet is a calcium antagonist similar to Ver. Its inhibitory effect on the tachycardia induced by Iso is due to its action on Ca which may be an essential modulator of the sequence of events linking β-adrenoceptor activation and heart rate response.
Keywords:
The pD’ values of Tet and Ver were 6.48±0.45 and 4.30±0.18, respectively. Hence the antagonistic effect of Ver was stronger than that of Tet. The pA of propranolol=7.86+0.21.
Tet and Ver antagonized the positive chronotropic responses to Ca (3.3 mM) in spontaneously beating rabbit atria.
It is proposed that Tet is a calcium antagonist similar to Ver. Its inhibitory effect on the tachycardia induced by Iso is due to its action on Ca which may be an essential modulator of the sequence of events linking β-adrenoceptor activation and heart rate response.