Aim: To explore the action of doxorubicin on vascular smooth muscle cells.
Methods: Isometric tension of denuded or intact thoracic aortic vessels was recorded and [Ca(2+)](i) in isolated aortic smooth muscle cells was measured by using Fluo-3.
Results: Doxorubicin induced phasic and tonic contractions in denuded vessels and increased levels of [Ca(2+)](i) in single muscle cells. Treatment with 10 micromol/L ryanodine had no effect on basal tension, but it did abolish doxorubicin-induced phasic contraction. Treatment with 10 mmol/L caffeine induced a transient phasic contraction only, and the effect was not significantly altered by ryanodine, the omission of extracellular Ca(2+) or both. Phenylephrine induced rhythmic contraction (RC) in intact vessels. Treatment with 100 micromol/L doxorubicin enhanced RC amplitude, but 1 mmol/L doxorubicin abolished RC, with an increase in maximal tension. Caffeine at 100 micromol/L increased the frequency of the RC only. In the presence of 100 micromol/L caffeine, however, 100 micromol/L doxorubicin abolished the RC and decreased its maximal tension. Treatment with 10 micromol/L ryanodine abolished the RC, with an increase in the maximal tension. In Ca(2+)-free solution, doxorubicin induced a transient [Ca(2+)](i) increase that could be abolished by ryanodine pretreatment in single muscle cells. The doxorubicin-induced increase in [Ca(2+)](i) was suppressed by nifedipine and potentiated by ryanodine and charybdotoxin.
Conclusion: Doxorubicin not only releases Ca(2+) from the sarcoplasmic reticulum but also promotes the entry of extracellular Ca(2+) into vascular smooth muscle cells.