Effect of S1P on S1P receptor desensitization in WT and PKCε-null adult cardiomyocytes. Adult cardiomyocytes were isolated from WT and PKCε-null mouse hearts. Quiescent cardiomyocytes were preincubated with 100 nM S1P for 1 hour (A) or overnight (B), then stimulated with a second pulse of 100 nM S1P for 10 minutes. Cells were then harvested and Western blot analysis was performed with the indicated antibodies. pERK, phosphorylated p42/44 MAPK; tERK, total p42/44 MAPK; WT, wild-type cells; and PKCε KO, PKCε-null cells. Data are expressed as mean ± SEM of 3 independent experiments. *P < 0.05 compared with all other values. o/n, overnight.