Biophys J, December 1999, p. 2988-2998, Vol. 77, No. 6

Barium Inhibition of the Collapse of the Shaker K⁺ Conductance in Zero K⁺

Departamento de Reconocimiento Molecular y Biologia Estructural, Instituto de Biotecnologia, UNAM, Cuernavaca, Morelos 62250, and Departamento de Fisiologia, Facultad de Medicina, UNAM, D.F. 04510, Mexico

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 (Gómez-Lagunas, 1997, J. Physiol. (Lond.). 499:3-15). Here it is shown that 1) Ba²⁺ impedes the collapse of the K⁺ conductance, protecting it from both sides of the membrane; 2) external Ba²⁺ protection (K_d = 63 µM at 80 mV) decreases slightly as the holding potential (HP) is made more negative; 3) external Ba²⁺ cannot restore the previously collapsed conductance; on the other hand, 4) internal Ba²⁺ (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). Ba²⁺ is an effective K⁺ substitute, inhibiting the passage of the channels into the stable nonconducting (noninactivated) mode of gating.

Biophys J, December 1999, p. 2988-2998, Vol. 77, No. 6
© 1999 by the Biophysical Society   0006-3495/99/12/2988/11  $2.00

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