Aim To investigate the effects of magnesium lithospermate B(MLB) on
vasoconstriction of denuded aortic rings in vitro,as well as the effects of MLB on cytosolic free calcium concentration(
_i) in aortic vascular smooth muscle cells(AVSMCs).Methods Isotonic tension was measured in the rat thoracic aortic rings without endothelium and quantitative changes of _i were directly monitored in AVSMCs loaded with the fluorescent calcium indicator Fluo-3 using intracellular cation measurement system.Results MLB had no effects on resting ring tension in the presence or absence of extracellular Ca~(2+).In rings exposed to 50～200 μmol·L~(-1) MLB,the isotonic contractions induced by 1 μmol·L~(-1) PE were decreased in calcium-free K-H solution.However,in the presence of extracellular Ca~(2+),KCl 60 mmol·L~(-1) produced isotonic contractions that were abolished by verapamil 10 μmol·L~(-1) or inhibited by pretreatment of 50～200 μmol·L~(-1) MLB in a concentration-dependent manner.When administered to the rings precontracted with 1 μmol·L~(-1) PE in the absence of extracellular Ca~(2+),a second extracelluar-calcium-dependent vasoconstriction induced by restoration of extracellular Ca~(2+) was also reduced by pretreatment of 50～200 μmol·L~(-1) MLB.Moreover,MLB,at concentration of 50～200 μmol·L~(-1),produced little effect on AVSMCs _i in the presence or absence of extracellular Ca~(2+).In AVSMCs exposed to 50～200 μmol·L~(-1) MLB,the inhibitory effects of MLB on _i induced by 20 μmol·L~(-1) ATP were concentration-dependent,with decreases ranging from 17.4% to 61.1% in the absence of extracellular Ca~(2+).In the presence of extracellular Ca~(2+) and thapsigargin,the increases in AVSMCs _i evoked by 60 mmol·L~(-1) KCl were inhibited by pretreatment with MLB(50～200 μmol·L~(-1)) or abolished by pretreatment with verapamil(10 μmol·L~(-1)).Conclusions MLB inhibits vasoconstriction induced by PE,high-K~+,and re-Ca~(2+).MLB also has inhibitory effects on increase of _i induced by ATP and high K~+ in AVSMCs.These results indicate that both the blocking effects on calcium release and voltage-dependent calcium channels may be responsible for the effects of MLB on _i in vascular smooth muscle cells.
More abstracts about the Magnesium lithospermate B inhibits intracellular calcium elevation induced by ATP and KCl in rat vas