| To define the importance of receptor phosphorylation and beta arrestin binding in desensitization , and to determine whether beta arrestin binding and receptor endocytosis are required for receptor dephosphorylation , we expressed TRH receptors in fibroblasts from mice lacking beta arrestin 1 and / or beta arrestin 2 . ^^^ At 30 min , endogenous beta arrestins reduced TRH stimulated inositol phosphate production by 48 % ( beta arrestin 1 ) , 71 % ( beta arrestin 2 ) , and 84 % ( beta arrestins 1 and 2 ) . ^^^ |