Different blocking effects of Cd++ and Hg++ on the early outward current in myocardial mouse cells.
The effects of external Cd++ and Hg++ on the early outward current (IEO) in myocardial mouse cells were studied using voltage clamp with one suction pipette. Both Cd++ in the millimolar and Hg++ in the micromolar range shifted the half time to peak IEO to positive potentials more than the current amplitude after 50 ms. Incomplete blocking of IEO could be obtained by Cd++ concentrations between 10(-3) and 2 x 10(-2) mol/l and by Hg++ concentrations between 10(-6) and 5 x 10(-5) mol/l. The current-voltage relationships of IEO at peak time and at 50 ms were mainly shifted to the right by Cd++ whereas Hg++ mainly decreased the slope. At incomplete blocking concentrations Cd++ slowed down IEO activation more strongly than did Hg++. All Cd++ effects were completely reversible. The action of Hg++ was irreversible. It is concluded that both ions act directly on the gating machinery of the channels rather than simply binding to homogenous surface charges.
Benndorf
K
K
Julius Bernstein Institute of Physiology, Martin Luther University Halle-Wittenberg, GDR.
Nilius
B
B
D000200:Action Potentials / Q000187:drug effects; D000818:Animals; D002104:Cadmium / Q000494:pharmacology*; D006321:Heart / Q000187:drug effects*; D066298:In Vitro Techniques; D008628:Mercury / Q000494:pharmacology*; D051379:Mice; D009206:Myocardium / Q000166:cytology / Q000378:metabolism; D015221:Potassium Channels / Q000187:drug effects / Q000378:metabolism
D015221:Potassium Channels; D002104:Cadmium; D008628:Mercury