TABLE 1

Effect of receptor density on potency of 5-HT at 5-HT_4(b) and 5-HT_7(a) receptors The amount of cAMP accumulated during 5-min exposure to increasing concentrations of 5-HT (8 pM to 50 μM) was measured in intact EcR293 cells expressing either the 5-HT_4(b) or 5-HT_7(a) receptor at low and high receptor densities. cAMP levels were measured, and the pEC₅₀ value was calculated as described under Materials and Methods. Data shown are the mean ± S.E.M. from three (5-HT₇) and four (5-HT₄) experiments.