INACTIVATION IN SHAKERB K- A TEST FOR THE NUMBER OF INACTIVATING PARTICLES ON EACH CHANNEL( CHANNELS )

Fast inactivation in ShakerB K channels results from pore-block caused by ''ball peptides'' attached to the inner part of each K channel. We have examined the question of how many functional inactivating balls are on each channel and how this number affects inactivation and recov ery from inactivation. To that purpose we expressed ShakerB in the ins ect cell line Sf9 and gradually removed inactivation by perfusing the cell interior with the hydrolytic enzyme papain under whole cell patch clamp. Inactivation slows down as the balls are removed by an amount consistent with the presence of four balls on each channel. Recovery f rom inactivation has the same time course early and late in papain act ion; it does not depend on the number of balls remaining on the channe l, consistent with the idea that reinactivation is not significant dur ing recovery from inactivation. Our conclusion is that ShakerB has fou r ball peptides, each capable of causing inactivation. Statistically, the balls are identical and independent. The stability of N-type inact ivation by the remaining balls is not appreciably affected by removing some of the balls from a channel.