Figure 3.

Functional and pharmacologic characterization of KvLQT1 currents in Xenopus oocytes. (a) Families of currents from water- and KvLQT1-injected oocytes were elicited by 1-sec voltage steps from a holding potential of −80 mV to test potentials ranging from −100 to +40 mV in 10 mV increments. (b) Peak current-voltage (I-V) relationship for 12 oocytes expressing KvLQT1. Currents were recorded using the protocol in a. (c) Dependence of tail current reversal potential (E_rev) on the external K⁺ concentration. Tail currents were elicited at potentials of −110 to +10 mV after a pulse to +20 mV (n = 6 oocytes), while the external K⁺ concentration was varied between 2, 10, 40, and 98 mM. E_rev under each condition was determined for each oocyte by measuring the zero intercept from a plot of tail current amplitude versus test potential. The dashed line has a slope of 58 mV and is drawn according to the Nernst equation for a perfectly selective K⁺ channel. Data are the mean ± SEM from six experiments. (d) Effects of E-4031, 4-aminopurine, tetraethylammonium, and clofilium on KvLQT1 current. Superimposed currents were recorded during 500-ms steps to +30 mV, from −80 mV, during the same experiment. Compounds were applied via bath perfusion in order from top to bottom. The bath was perfused with control solution for 5 min, or until effects reversed completely, between compounds. (e) Effects of cAMP on KvLQT1 currents. Currents were recorded using the protocol in a before and 10 min after the simultaneous addition of 10 μM forskolin and 100 μM IBMX to the bath.