The mechanism of antiarrhythmic effects of palmatine( Pal), an benzoquinolizine compound were studied in experimental animals.In the isolated guinea pig papillary muscles, Pal 50 ?mol/L markedly prolonged the functional refractory period(FRP)and decreased the automaticity induced by adrenaline, but exerted no effect on excitabj- iity and contractility of the muscles.Pal(10 ?mol/L ) prolonged both APD20 and APD90 of the action potential of guinoa pig papillary muscles. The Vmax was decreased at 100 ?mol/L Pal, but the action potential amplitude( APA ) and resting potential ( RP ) were unaltered.The antiarrhythmic action of Pal may be due to its ability to decrease automaticity and to proloagate FRP and APD of the myocardium.

Tetrandrine, a bis-benzy 1-i soqui noline alkaloid isolated from Radix Stephania tetrandra S. Moor, was proved to be a calcium antagonist. Its effects upon the heart conduction system were investigated in anesthetized rabbits.Tetrandrine 8 mg/kg iv could prolong the sino-atrial conduction time & the sinus node recovery time from 50 ? 13 ms & 286? 36 ms to 75?19 ms ( n= 8 , P

Jat(lOmg/kg iv) administered 5 min prior to ligation of left anterior descending coronary artery significantly decreased the incidence of arrhy-thmias(VT and VF)and mortality of rats during ischaemia and reper-fusion.It also delayed the onset and shortened the duration of arrhythmias. The size of myocardial infarction caused by coronary artery ligation was decreased by Jat ( 0.75mg/kg iv. 1 h before and 6 h after operation) in rabbits.

Berberine could reverse the phenylephrine-induced contraction of aortic strips of rabbits, but not those induced by histamine, serotonin and high-K. It showed no effect on the resting tension of the strips.Prazosin l ?M completely abolished the phenylephrine-induced contraction of the strips, but berberine 100 ?M could block 94 ? 9%.The IC50 of berberine and prazosin for phenylephrine-induced c-ontraction is 30 ?M and 0.2 ?M. The results suggest that the action of berberine is not similar to sodium nitroprusside, but is similar to prazosin, a selective ?1 adrenoceptor blocker, although its potency is less than prazosin.