In the above article [Cladman W and Chidiac P (2002)Mol Pharmacol 62:654–659], there were two errors.

In the first error, the equation under Materials and Methodswas incorrect. It should have read:

y = ns + max₁[x]/(K _up+ [x]) + max₂[x]/(K _down+ [x])

In the second error, the legend to Fig. 5 was incorrect. The corrected text of the legend appears below:

Fig. 5. Concentration dependence of RGS2 and RGS4 GAP activities at high and low magnesium levels. Agonist-dependent GTPase activities were measured in the presence of 0.5 mM (A) and 7.5 mM (B) calculated free Mg²⁺ (total added MgCl₂ was 2 mM and 10 mM, respectively) in the absence of RGS protein (○) or at the RGS2 (▴) and RGS4 (▪) concentrations indicated on the abscissae. Data were fitted to either eq. 1 (RGS4 in A) or the Hill equation (others), and average parameters from these and replicate data sets are presented in Table 1.

We regret these errors and apologize for any confusion or inconvenience they may have caused.

• The American Society for Pharmacology and Experimental Therapeutics