The products of the mdr1a and mdr1b genes from multidrug resistant murine cells have similar degradation rates.

Two vinblastine-resistant sublines of the murine macrophage-like cell line J774.2, J7.V1-1 and J7.V3-1, overproduce unique forms of P-glycoprotein that are encoded by distinct mdr genes, mdr1b and mdr1a, respectively. Degradation rates of the two P-glycoprotein isoforms were measured by immunoprecipitation of P-glycoprotein. The half-life of immunoprecipitable P-glycoprotein from J7.V1-1 cells was 16.8 +/- 0.5 hours and from J7.V3-1 cells, 17.4 +/- 0.5 hours. This rate was not influenced by the presence of vinblastine in the growth medium. The data indicate that P-glycoproteins derived from distinct genes have similar degradation rates.