[Barium ion blockade on an inward rectifying potassium current in oocytes of the frog Xenopus laevis].
The effect of barium (Ba2+) on inward rectifier K+ current endogenous (IRK-endo) was characterized in Xenopus laevis oocytes with two microelectrodes voltage clamp technique. Varying [K+]o caused a shift in the reversal potential and a change in the straight pert of the slope as expected for K+ current. External Ba2+ blocked IRK-endo displayed lower affinity in the channel in two different forms. The blockade of the peak current was voltage independent, and had a Kd of 0.9 +/- 0.1 mM. In contrast, a second effect on the late current (80 ms). Was both time and voltage dependent, with a Kd that display monoexponential voltage dependence (tau = 50 +/- mV.) These observations suggest the presence of two different binding sites for Ba2+, one in the external vestibule of the channel and another lying within the channel. Our results demonstrate the existence of an endogenous K+ current in Xenopus laevis oocytes with characteristics that resemble other inward rectifier K+ channels found in other species.
Gamboa
R
R
Departamento de Fisiología, Instituto Nacional de Cardiología Ignacio Chávez, México, D.F.
Martínez
M
M
Cumming
E
E
D000818:Animals; D001464:Barium / Q000494:pharmacology*; D003864:Depression, Chemical; D004305:Dose-Response Relationship, Drug; D005260:Female; D009865:Oocytes / Q000187:drug effects* / Q000502:physiology; D018408:Patch-Clamp Techniques / Q000295:instrumentation; D015221:Potassium Channels / Q000187:drug effects* / Q000502:physiology; D013997:Time Factors; D014982:Xenopus laevis
D015221:Potassium Channels; D001464:Barium