[Effects of alpha-adrenoreceptor excitation on the delayed after-depolarization of sheep cardiac Purkinje fibers].
By using acetyl strophanthidin (AS) 0.2 mumol/L, the delayed after-depolarization (DAD) was induced in sheep cardiac Purkinje fibers and recorded with intra-cellular microelectrode. When beta-adrenoceptor was blocked by propranolol 1.0 mumol/L, phenylephrine 1.0 mumol/L increased the amplitude of DAD from 8.1 +/- 2.2 mV to 9.5 +/- 2.8 mV, prolonged the duration of DAD from 240 +/- 47 ms to 273 +/- 47 ms (n = 13, P < 0.01) and increased the up rising velocity of DAD from 0.039 +/- 0.023 V/s to 0.051 +/- 0.026 V/s (n = 13, P < 0.05). The DAD occurred earlier for 30 +/- 47 ms to preceding action potential (n = 13, P < 0.05). When triggered action potentials were induced by norepinephrine 1.0 mumol/L on the basis of DAD, propranolol 1.0 mumol/L could suppress the triggered beats while phentolamine 1.8 mumol/L showed little effect. The above results indicate that excitation of alpha-receptor had only slight augmentation effect on DAD. However, for the triggered activity induced by DAD, the inhibitory effect of beta-blockers are stronger than that of alpha-blockers.
Bao
R D
RD
Shanghai Second Medical University.
Li
C Z
CZ
Liu
Y M
YM
Xu
Y Q
YQ
D000200:Action Potentials / Q000187:drug effects; D000316:Adrenergic alpha-Agonists / Q000494:pharmacology*; D000818:Animals; D004562:Electrocardiography; D008839:Microelectrodes; D010656:Phenylephrine / Q000494:pharmacology; D011433:Propranolol / Q000494:pharmacology; D011690:Purkinje Fibers / Q000502:physiology*; D011942:Receptors, Adrenergic, alpha / Q000187:drug effects; D012756:Sheep; D013327:Strophanthidin / Q000031:analogs & derivatives / Q000494:pharmacology
D000316:Adrenergic alpha-Agonists; D011942:Receptors, Adrenergic, alpha; D010656:Phenylephrine; D013327:Strophanthidin; D011433:Propranolol; C004681:acetylstrophanthidin