cAMP-dependent protein kinase activation affects vasopressin V₂-receptor number and internalization in LLC-PK₁ renal epithelial cells

The relationship between activation of the cAMP-dependent protein kinase (cAMP-PK) and ligand binding and internalization by the vasopressin renal (V₂-type) receptor of LLC-PK₁ renal epithelial cells was examined. Upon cAMP-PK activation through 1 h treatment with the cAMP analogue 8-bromo-cAMP (BrcA), a marked reduction in V₂-receptor steady state number and internalization in LLC-PK₁ cells was effected. In cells treated for 17 h with BrcA and hence down-regulated for cAMP-PK₁ the V₂-receptor number was normal but internalization was markedly reduced. Cells of the LLC-PK₁ mutant FIB4, which possesses about 10% parental cAMP-PK catalytic subunit activity, exhibited lower V₂-receptor steady state number and internalization in comparison to untreated LLC-PK₁ cells. A negative correlation was thus evident between cAMP-PK activation and V₂-receptor number and internalization. Phosphorylation by cAMP-PK may effect ligand-independent removal of receptor from the plasma membrane.