Table 3

Internalization and rates of down-regulation induced by various concentrations of fenoterol, a strong agonist

[Fenoterol]	Fraction Occupied	Fraction Receptor Internalized	k_deg Fraction Lost/h	S.E.
2 μM	0.93	0.49 (±0.02)	0.226	0.02
200 nM	0.58	0.40 (±0.04)	0.170	0.03
20 nM	0.12	0.09 (±0.05)	0.109	<0.01
2 nM	0.014	<0.01	0.075	0.02
0.2 nM	0.0014	<0.01	0.045	0.01

Agonist was applied at concentrations that resulted in occupancies shown in the first column. Extent of receptor internalization is shown in the second column (n = 3; ±S.E.M.). Rates of down-regulation (k _deg), presented as the fraction of remaining receptor lost per hour are given, as generated by GraphPad software using eqs. 3 and 6 as explained under Experimental Procedures, along with standard errors.