Barium inhibition of the collapse of the Shaker K(+) conductance in zero K(+).
In the absence of K(+) on both sides of the membrane, delivery of standard activating pulses collapses the Shaker B K(+) conductance. Prolonged depolarizations restore the ability to conduct K(+). It has been proposed that the collapse of the conductance results from the dwelling of the channels in a stable closed (noninactivated) state (, J. Physiol. (Lond.). 499:3-15). Here it is shown that 1) Ba(2+) impedes the collapse of the K(+) conductance, protecting it from both sides of the membrane; 2) external Ba(2+) protection (K(d) = 63 microM at -80 mV) decreases slightly as the holding potential (HP) is made more negative; 3) external Ba(2+) cannot restore the previously collapsed conductance; on the other hand, 4) internal Ba(2+) (and K(+)) protection markedly decreases with hyperpolarized HPs (-80 to -120 mV), and it is not dependent on the pulse potential (0 to +60 mV). Ba(2+) is an effective K(+) substitute, inhibiting the passage of the channels into the stable nonconducting (noninactivated) mode of gating.
Gómez-Lagunas
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Departamento de Reconocimiento Molecular y Biologia Estructural, Instituto de Biotecnologia, UNAM, Cuernavaca, Morelos 62250, Mexico. froylan@ibt.unam.mx
D000818:Animals; D001464:Barium / Q000494:pharmacology; D055592:Biophysical Phenomena; D001703:Biophysics; D002460:Cell Line; D004553:Electric Conductivity; D066298:In Vitro Techniques; D008564:Membrane Potentials; D011188:Potassium / Q000494:pharmacology; D026902:Potassium Channel Blockers; D015221:Potassium Channels / Q000235:genetics / Q000378:metabolism*; D011994:Recombinant Proteins / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism; D051637:Shaker Superfamily of Potassium Channels; D012996:Solutions; D018411:Spodoptera
D026902:Potassium Channel Blockers; D015221:Potassium Channels; D011994:Recombinant Proteins; D051637:Shaker Superfamily of Potassium Channels; D012996:Solutions; D001464:Barium; D011188:Potassium