Effect of PKC inhibition on ERK activation via the LPA receptor and the m5-muscarinic receptor (A + B). Effect of βARKct on LPA-mediated ERK activation in L cells (C). Quiescent L cells were pretreated with DMSO or with 100 ng/ml TPA for 16 h (A and B) or not pretreated at all (C). The cells were then stimulated as indicated with agonists [1% BSA (control, CO), 25 μM LPA, or 100 nM carbachol (Cch), 100 ng/ml TPA], lysed and subjected to an ERK mobility shift assay (see Materials and Methods). (A and B) After a 5-min incubation of cells with 1% BSA (control, CO), 25 μM LPA, or 100 ng/ml TPA, ERK activation was compared in L cells stably transfected with vector alone or with the βARKct plasmid (C).