. "Here we describe the basic features of the interaction of K+ channels with Pi1, a recently described 35 amino acid scorpion toxin, which has four disulfide bridges instead of the three commonly found in all the other known scorpion toxins. We found that: (a) Pi1 blocks ShakerB from the outside with a 1:1 stoichiometry, and a Kd of 32 nM in zero external [K+]; (b) extracellular K+, Rb+ and Cs+ but not NH4+ ions strongly impede (destabilize) the block by this toxin; interestingly (c) the destabilizing binding of K+, Rb+, and Cs+ is described by a Hill coefficient n > 1; (d) external K+ is more effective than internal K+ to reduce the block by Pi1." . . "FEBS Lett." . "Possani L.D." . "Olamendi-Portugal T." . "Gomez-Lagunas F." . "1997"^^ . "197-200" . "Block of ShakerB K+ channels by Pi1, a novel class of scorpion toxin." . "400" . "doi:10.1016/S0014-5793(96)01387-7" .