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Abstract:
Incorporated terbium, Tb3+, activates the Ca‐activated K channel found in the resealed erythrocyte ghost membrane and allows the net efflux of K. As in the case of Ca activation, low levels of external K stimulate the net efflux of K. The action of incorporated Tb3+ seems to be analogous to that of incorporated Ca.
Externally applied Tb3+, however, inhibits the net efflux of K after either Ca or Tb3+ activation. The net‐efflux of K can be inhibited by Tb3+ even after partial digestion of the channel by low levels of incorporated trypsin. Furthermore, the channel when incorporated into planar bilayers, can be inhibited by Tb3+. Externally applied Tb3+ does not seem to inhibit net K efflux indirectly via inhibition of the pathways for the co‐transported anions. In addition because of the low concentrations of Tb3+ required for inhibition, it seems unlikely that an alteration of surface potential is responsible for the observed effects.
