BACKGROUND: Batroxobin (BX), a serine protease used in defibrinogenation and thrombolysis, also has an effect on c-fos gene and growth factor. This study attempted to determine the effects of BX on the proliferation of vascular smooth muscle cells (VSMCs) and calcium metabolism. METHODS: VSMCs were treated with BX at concentrations of 0.1, 0.3, or 1.0 mmol/L and cell numbers were determined at 0, 24, 48, and 72 hours. Intracellular calcium concentration ([Ca2+]i) was measured using direct fluorescence methods. RESULTS: BX was found to suppress proliferation of VSMCs in a dose-dependent fashion with inhibition rates of 18% and 31% by 48 and 72 hours, respectively. In addition, BX decreases basal [Ca2+]i significantly. The basal level in untreated cells was 162.7 +/- 33.8 nmol/L, and decreased to 131.5 +/- 27.7 nmol/L, 128.3 +/- 28.5 nmol/L, and 125.6 +/- 34.3 nmol/L with the three concentrations of BX, respectively. Noradrenaline (NE)-induced [Ca2+]i stimulation was also attenuated by BX (0.1 mmol/L BX, 20% +/- 8% inhibition; 0.3 mmol/L BX, 54% +/- 11% inhibition; 1.0 mmol/L BX, 62% +/- 15% inhibition). The ability of NE to stimulate [Ca2+]i was attenuated in cultures in Ca(2+)-free medium, as was the ability of BX to blunt NE-induced stimulation. CONCLUSION: These findings demonstrate that BX can effectively inhibit proliferation of VSMCs, probably by blocking the release and uptake of Ca2+, thus influencing [Ca2+]i.