INTERNAL BLOCKADE OF A CA2+-ACTIVATED K+ CHANNEL BY SHAKER-B INACTIVATING BALL PEPTIDE

Shaker B inactivating peptide ("ball peptide", BP) interacts with Ca2+-activated K+ (K(Ca)) channels from the cytoplasmic side only, producing inhibition of channel activity. This effect was reversible and dose and voltage dependent (stronger at depolarized potentials). The inhibition of K(Ca) channels by BP cannot be mimicked by an inactive point mutation of the BP, L7E. BP binds to K(Ca) channels in a bimolecular reaction (dissociation constant of 95-mu-M at +40 mV). The binding site is probably located in the internal "mouth" or conduction pathway, since both external K+ and internal tetraethylammonium relieve BP-induced inhibition. These results suggest that K(Ca) channels possess a binding site for the BP with some properties similar to the ball receptor found in Shaker B K+ channels.