A delayed rectifier potassium current in Xenopus oocytes.
A delayed voltage-dependent K+ current endogenous to Xenopus oocytes has been investigated by the voltage-clamp technique. Both activation and inactivation of the K+ current are voltage-dependent processes. The K+ currents were activated when membrane potential was depolarized from a holding potential of -90 to -50 mV. The peak current was reached within 150 ms at membrane potential of +30 mV. Voltage-dependent inactivation of the current was observed by depolarizing the membrane potential from -50 to 0 mV at 10-mV increments. Voltage-dependent inactivation was a slow process with a time constant of 16.5 s at -10 mV. Removal of Ca2+ from the bath has no effect on current amplitudes, which indicates that the current is Ca2+)-insensitive. Tail current analysis showed that reversal potentials were shifted by changing external K+ concentration, as would be expected for a K(+)-selective channel. The current was sensitive to quinine, a K+ channel blocker, with a Ki of 35 microM. The blockade of quinine is voltage-independent in the range of -20 to +60 mV. Whereas oocytes from the same animal have a relatively homogeneous current distribution, average amplitude of the K+ current varied among oocytes from different animals from 30 to 400 nA at membrane potential of +30 mV. Our results indicate the presence of the endogenous K+ current in Xenopus oocytes with characteristics of the delayed rectifier found in some nerve and muscle cells.
Lu
L
L
Department of Physiology, Johns Hopkins University School of Medicine, Baltimore, Maryland 21205.
Montrose-Rafizadeh
C
C
Hwang
T C
TC
Guggino
W B
WB
D000818:Animals; D004553:Electric Conductivity; D004558:Electric Stimulation; D005260:Female; D066298:In Vitro Techniques; D007700:Kinetics; D008564:Membrane Potentials / Q000187:drug effects; D008839:Microelectrodes; D009865:Oocytes / Q000502:physiology*; D011188:Potassium / Q000494:pharmacology; D015221:Potassium Channels / Q000187:drug effects / Q000502:physiology*; D011803:Quinine / Q000494:pharmacology; D014982:Xenopus laevis
D015221:Potassium Channels; D011803:Quinine; D011188:Potassium