Pertussis toxin does not block GC-B desensitization by 100 nM S1P or by 1% fetal bovine serum. GC-B/3T3 cells were incubated where indicated with 100 ng/ml pertussis toxin for 24 h prior to a 30 min incubation with 100 nM S1P or 1% fetal bovine serum as indicated. CNP responses following these treatments were determined as described under Methods. Results are the mean of duplicate observations -/+ the range of duplicates. Inset, cells were incubated for 10 min following pertussis treatment as described above and the levels of pERK and pAkt were determined as described under Methods.