Table 1.

Parameters for the nicotine-dose dependence (EC₅₀ values) and kinetics (τ values) for upregulation (onset and reversal) of native and heterologously expressed nAChR subtypes obtained from the relevant equation fit to the data (see Figs. 1B, 2A,B legends)

	Nicotine dose dependence (EC50)	Upregulation onset with nicotine addition		Upregulation reversal with nicotine removal
		τ1 (h)	τ2 (h)	τ1 (h)	τ2 (h)
α4β2	a2.7×10−7		14.5a	0.76	44
Surface			∼15a	1.2	45
α6β2	b4.6×10−5	b1.2	ND	0.94	∼500
α3β2	b1.3×10−4	b1.5	ND	ND	ND
Cortical neurons	9.2×10−8	1.1	12.5	0.45	295

Dose dependence of upregulation was measured by treating the HEK cells expressing nAChR subtypes or primary cultures of cortical neurons with increasing concentrations of nicotine and measuring increases in ¹²⁵I-epi binding. Onset of upregulation was measured by treating cells with appropriate concentrations of nicotine as determined through dose dependence and measuring increases in ¹²⁵I-epi binding as a function of time. Reversal of upregulation was initiated by treating the cells with appropriate concentrations of nicotine that cause maximum upregulation, washing the cells to remove nicotine, maintaining them in nicotine-free media, and measuring the ¹²⁵I-epi binding as a function of time. ND, Not determined.

^aTaken from Vallejo et al. (2005).

^bTaken from Walsh et al. (2008).