Multidrug resistance protein 4 mediates cAMP efflux from rat preglomerular vascular smooth muscle cells.

摘要

1. Previous studies have shown that stimulation of adenylyl cyclase in preglomerular vascular smooth muscle cells (PGVSMC) increases extracellular cAMP; however, the mechanism by which PGVSMC transport intracellular cAMP into the extracellular milieu is unknown. 2. We hypothesize that multidrug resistance protein (MRP) 4 is the primary transporter mediating efflux of intracellular cAMP from PGVSMC. 3. Both reverse transcription-polymerase chain reaction and real-time polymerase chain reaction detected MRP4 mRNA in PGVSMC in culture. Moreover, western blotting using an antibody specific for MRP4 gave rise to a 150 kDa signal, consistent with the presence of MRP4 protein in PGVSMC. 4. Specifically designed short interference (si) RNA reduced MRP4 mRNA expression by 71% (P = 0.0075) and MRP4 protein by 80% (P = 0.0004). 5. Isoproterenol (1 micromol/L) increased intracellular cAMP, which resulted in efflux of cAMP into the medium. The siRNA knockdown of MRP4 significantly reduced basal extracellular cAMP and nearly abolished isoproterenol-induced increases in extracellular cAMP (P = 0.0143, interaction between isoproterenol and MRP4 siRNA in two-factor analysis of variance). In isoproterenol-treated cells, MRP4 siRNA decreased the ratio of extracellular cAMP to intracellular cAMP by 72% (P = 0.0019). 6. We conclude that MRP4 is the dominant cAMP transporter in PGVSMC.