Do voltage-dependent K+ channels require Ca2+? A critical test employing a heterologous expression system.
Removal of Ca2+ from the solution bathing neurons is known in many cases to alter the gating properties of voltage-dependent K+ channels and to induce a large, nonselective "leak" conductance. We used a heterologous expression system to test whether the leak conductance observed in neurons is mediated by voltage-dependent K+ channels in an altered, debased conformation. Voltage-dependent K+ channels were expressed in an insect cell line infected with a recombinant baculovirus carrying the cDNA for Drosophila Shaker "A-type" K+ channels. These expressed channels respond to low Ca2+ identically to voltage-dependent K+ channels in native neuronal membranes; upon removal of external Ca2+, Shaker K+ currents disappear and are replaced by a steady, nonselective leak conductance. However, control cells devoid of Shaker channels were free of any voltage-dependent conductances and did not generate a leak when external Ca2+ was removed. These results show that Ca2+ is essential for proper function of voltage-dependent K+ channels and is required to stabilize the native conformations of these membrane proteins.
Armstrong
C M
CM
Department of Physiology, University of Pennsylvania School of Medicine, Philadelphia 19104.
Miller
C
C
D000818:Animals; D002118:Calcium / Q000494:pharmacology*; D002460:Cell Line; D002462:Cell Membrane / Q000502:physiology; D004330:Drosophila / Q000235:genetics; D004594:Electrophysiology / Q000379:methods; D007313:Insecta; D008564:Membrane Potentials; D008565:Membrane Proteins / Q000235:genetics / Q000502:physiology*; D015221:Potassium Channels / Q000187:drug effects / Q000502:physiology*
D008565:Membrane Proteins; D015221:Potassium Channels; D002118:Calcium