Voltage-dependence of virus-encoded miniature K+ channel Kcv.
Kcv is a K+-selective channel encoded by the Paramecium bursaria Chlorella virus 1 (PBVC-1). Expression of this protein, so far the smallest known functional K+ channel, in Xenopus oocytes reveals an instantaneous and a time-dependent component during voltage-clamp steps. These two components have an identical sensitivity to the inhibitor amantadine, implying that they reflect distinct kinetic features of the same channel. About 70% of the channels are always open; at hyperpolarizing voltages the time-dependent channels (30%) open in a voltage-dependent manner reaching half-maximal activation at about ?70 mV. At both extreme positive and negative voltages the open-channel conductance decreases in a voltage-dependent manner. To examine the mechanism underlying the voltage-dependence of Kcv we neutralized the two charged amino acids in the lipophilic N-terminus. However, this double mutation had no effect on the voltage-dependence of the channel, ruling against the possibility that these charged amino acids represent a membrane-embedded voltage sensor. We have considered whether a block by external divalent cations is involved in the voltage-dependence of the channel. The Kcv current was increased about 4-fold on reduction of external Ca2+ concentration by a factor of ten. This pronounced increase in current was observed on lowering Ca2+ but not Mg2+ and was voltage-independent. These data indicate a Ca2+-selective, but voltage-independent mechanism for regulation of channel conductance.
Gazzarrini
S
S
Department of Biology, CNR-Centro per la Biologia Molecolare e Cellulare delle Piante, Università degli Studi di Milano, via Celoria 26, 20133 Milan, Italy.
Etten
J L
JL
DiFrancesco
D
D
Thiel
G
G
Moroni
A
A
D000818:Animals; D002462:Cell Membrane / Q000502:physiology*; D002999:Clone Cells; D004553:Electric Conductivity; D005786:Gene Expression Regulation / Q000502:physiology; D008564:Membrane Potentials / Q000502:physiology*; D008954:Models, Biological; D009865:Oocytes / Q000502:physiology; D015221:Potassium Channels / Q000502:physiology*; D024642:Potassium Channels, Voltage-Gated / Q000502:physiology*; D012680:Sensitivity and Specificity; D013329:Structure-Activity Relationship; D014764:Viral Proteins; D014982:Xenopus laevis / Q000502:physiology
C405463:Kcv potassium channel, Chlorella virus; D015221:Potassium Channels; D024642:Potassium Channels, Voltage-Gated; D014764:Viral Proteins