The presence of caveolin-3 was reinvestigated in smooth muscle cells in situ and in culture. Immunocytochemistry of aortic strips showed that both caveolins-1 and -3 are present, but that caveolin-3 is considerably less abundant and detected in only a fraction of the cells. Cultured smooth muscle cells of passage 4 or greater still expressed caveolin-1 but lacked caveolin-3, likely due to dedifferentiation. Cultures exposed to redifferentiation-inducing medium were found to re-express caveolin-3. The return of caveolin-3 protein in these cells was accompanied by a fourfold increase in cav-3 mRNA, as detected by quantitative PCR, suggesting that the loss of protein in untreated cells was due to transcriptional rather than translational inhibition. These results suggest that caveolin-3 has a specialized role associated with the differentiated state in certain types of smooth muscle cells. (C) 2003 Elsevier Science (USA). All rights reserved.