SURFACE-CHARGES OF K CHANNELS - EFFECTS OF STRONTIUM ON 5 CLONED CHANNELS EXPRESSED IN XENOPUS OOCYTES

The effects of strontium (Sr2+; 7-50 mM) on five different cloned rat K channels (Kv1.1 Kv1.5, Kv1.6, Kv2.1, and Kv3.4), expressed in oocyte s of Xenopus laevis, were investigated with a two-electrode voltage cl amp technique. The main effect was a shift of the G(K)(V) curve along the potential axis, different in size for the different channels, Kv1. 1 was shifted most and Kv3.4 least, 21 and 8 mV, respectively, at 50 m M. The effect was interpreted in terms of screening of fixed surface c harges. The estimated charge densities ranged from -0.37 (Kv1.1) to -0 .11 (Kv3.4) e nm(-2) and showed good correlation with the total net ch arge of tile extracellularly located amino acid residues of the channe l as well as with the change of a specific region (the loop between th e S5 segment and the pore forming segment). The estimated surface pote ntials were found to be linearly related to the activation midpoint po tential, suggesting a functional role for the surface charges.