Concaterners of brain Kv1 channel α subunits that give similar K+ currents yield pharmacologically distinguishable heteromers

At least five subtypes of voltage-gated (Kv1) channels occur in neurons as tetrameric combinations of different alpha subunits. Their involvement in controlling cell excitability and synaptic transmission make them potential targets for neurotherapeutics. As a prerequisite for this, we established herein how the characteristics of hetero-oligomeric K+ channels can be influenced by alpha subunit composition. Since the three most prevalent Kv1 subunits in brain are Kv 1.2, 1.1 and 1.6, new Kv1.6-1.2 and Kv1.1-1.2 concatenated constructs in pIRES-EGFP were stably expressed in HEK cells and the biophysical plus pharmacological properties of their K+ currents determined relative to those for the requisite homotetramers. These heteromers yielded delayed-rectifier type K+ currents whose activation, deactivation and inactivation parameters are fairly similar although substituting Kv 1.1 with Kv 1.6 led to a small negative shift in the conductance-voltage relationship, a direction unexpected from the characteristics of the parental homo-tetramers. Changes resulting from swapping Kv1.6 for Kv 1.1 in the concatemers were clearly discerned with two pharmacological agents, as measured by inhibition of the K+ currents and Rb+ efflux. alpha Dendrotoxin and 4-aminopyridine gave a similar blockade of both hetero-tetramers, as expected. Most important for pharmacological dissection of channel subtypes, dendrotoxin(k) and tetraethylammonium readily distinguished the susceptible Kv1.1-1.2 containing oligomers from the resistant Kv1.6-1.2 channels. Moreover, the discriminating ability of dendrotoxink was further confirmed by its far greater ability to displace I-125-labelled alpha dendrotoxin binding to Kv1.1-1.2 than Kv1.6-1.2 channels. Thus, due to the profiles of these two channel subtypes being found to differ, it seems that only multimers corresponding to those present in the nervous system provide meaningful targets for drug development. (C) 2007 Elsevier Ltd. All rights reserved.