Figure 8.
A positively charged residue at the M770 position abolishes the absolute requirement for ions. a, Superimposed family of membrane currents evoked by 1 mm l-Glu between −100 and +110 mV in Na+-free solutions. KARs with Met770 substituted with either an aliphatic (M770A; patch 06724p3) or an acidic (M770D; patch 06727p2) amino acid still have an absolute requirement for external ions. In contrast, substitution of Met770 with a positively charged amino acid (Arg; patch 06713p2) results in an outward current in Na+-free solutions (middle). b, Mean current–voltage plots from at least three experiments in physiological Na+ (150 mm; open triangles) and Na+-free (0 mm; filled circles) solution, demonstrating that GluR6M770R is functional, whereas GluR6M770A and GluR6M770D are nonfunctional.