RESUMEN
<p><b>OBJECTIVE</b>To explore the expression of origin recognition complex 1 (ORC1) during the DNA replication of vascular muscle cells (VSMC).</p><p><b>METHODS</b>VSMC of thoracic aorta in rats were obtained by the adherence method of tissue culture. The cell synchrony was obtained by the method of double-thymidine block, colchicine treatment and serum starvation. The expression of ORC1 mRNA at different cell cycles of VSMC was determined by RT-PCR and the protein expression of ORC1 was analyzed by Western blot.</p><p><b>RESULTS</b>Cultured VSMC were identified by light microscope and immunocytochemistry. Significant expression of ORC1 mRNA and protein in a quiescent stage of VSMC were not observed. Upon synchronization, the expression of ORC1 mRNA was significantly higher at G(1)/S phase of VSMC than that at S and G(2)/M phases. The expression of ORC1 protein followed same changes as the ORC1 mRNA expression at different stages of cell cycles.</p><p><b>CONCLUSION</b>ORC1 may be an important regulatory factor at the initiation of proliferative process of VSMC.</p>