[Effects of tetrahydroprotoberberines on cytosolic free calcium in cultured rat single myocardial cells].

Effect of tetrahydroberberine (THB), l-tetrahydropalmatine (THP) and l-stepholidine (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 cytosolic free calcium ([Ca2+]i) in cultured rat single myocardial cells were examined and compared with verapamil (Ver). THB, THP and SPD (10-100 mumol.L-1) were found to increase resting [Ca2+]i gently, which was not depressed by tetrodotoxin. THB, THP and SPD (1-100 mumol.L-1) were also shown to inhibit the KCl-induced [Ca2+]i elevation, the IC50 values of THB and SPD were 50.9 (95% confidence limits: 18.5-140) mumol.L-1 and 23.5 (95% confidence limits 7.6-73.4) mumol.L-1, respectively. THB, THP and SPD 30 mumol.L-1 were also shown to inhibit the elevation of [Ca2+]i induced by high extracellular calcium and norepinephrine; but the inhibitory effects of these drugs were weaker than those of Ver. The three compounds showed no significant effect on ouabain induced [Ca2+]i increase. 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.