Figure 3: Split channels retain dependence on the prepulse potential and on extracellular Mg²⁺.

(a,b) Representative current traces obtained following the depicted protocol, holding the oocyte for 5 s (indicated in the schematic as a dotted line) at the indicated potential and immediately stimulating to +40 mV in the absence (upper traces) or the presence (middle traces) of 5 mM extracellular Mg²⁺. Both wild-type (a) and split (b) channels show accelerated activation at less hyperpolarized potentials. Also in both cases, Mg²⁺ slows down the activation. The effect of prepulse potential at different Mg²⁺ concentrations is depicted in the lowest panels (n=5–8). Over 1 mM, the activation of the split channel is so slow that the dependence on prepulse is not any longer evident. The solid lines indicate fits to sigmoid functions, dotted lines represent polynomial fits. (c) Comparison of data (from a,b) of continuous and split channel in 1 mM Mg²⁺. (d) Effect of Mg²⁺ concentration on the speed of activation of continuous and split channels. The activation was slower in the split channels (closed symbols) than in control (open symbols) under all conditions tested. Error bars represent s.e.