EFFECTS OF TETRAHYDROPROTOBERBERINES ON CYTOSOLIC FREE CALCIUM IN CULTURED RAT SINGLE MYOCARDIAL CELLS

Effect of tetrahydroberberine(THB),l-tetrahydropalmatine(THP) and l-stepholi-dine(SPD) were supposed to be related to the blocking of calcium influx. In this paper,using Fura-2/AM and AR- CM-MIC cation measurement system,the effects of THB,THP and SPD on cytosolicfree calcium(Ca²⁺i) in cultured rat single myocardial cells were examined and compared withverapamil(Ver). TH,THP and SPD(10～100μmol·L^-1) were found to increase restingCa²⁺i gently,which was not depressed by tetrodotoxin. THB,THP and SPD(1～100μmol·L^-1)were also shown to inhibit the KCl- inducedCa2+i elevation, the IC50 values of THBand SPD were 50.9(95%confidence limits: 18.5～140)μmol·L^-1 and 23.5(95%confidencelimits 7.6～73.4)μmol·L^-1, respectively. THB, THP and SPD 30μmol·L^-1 were also shown toinhibit the elevation ofCa²⁺i induced by high extracellular calcium and norepinephrine; but theinhibitory effects of these drugs were weaker than those of Ver. The three compounds showed nosignificant effect on ouabain inducedCa²⁺i increas1e. These results suggest that the inhibitory effects of THB, THP and SPD on Ca²⁺i in myocite by blocking voltage- dependent calcium channels were similar but inferior to Ver.