Evidence for negative charge in the conduction pathway of the cardiac ryanodine receptor channel provided by the interaction of K+ channel N-type inactivation peptides.

We have investigated the interaction of two peptides (ShB - net charge +3 and ShB:E12KD13K - net charge +7) derived from the NH2-terminal domain of the Shaker K+ channel with purified, ryanodine-modified, cardiac Ca2+-release channels (RyR). Both peptides produced well resolved blocking events from the cytosolic face of the channel. At a holding potential of +60 mV the relationship between the probability of block and peptide concentration was described by a single-site binding scheme with 50% saturation occurring at 5.92 +/- 1.06 microM for ShB and 0.59 +/- 0. 14 nM for ShB:E12KD13K. The association rates of both peptides varied with concentration (4.0 +/- 0.4 sec-1 microM-1 for ShB and 2000 +/- 200 sec-1 microM-1 for ShB:E12KD13K); dissociation rates were independent of concentration. The interaction of both peptides was influenced by applied potential with the bulk of the voltage-dependence residing in Koff. The effectiveness of the inactivation peptides as blockers of RyR is enhanced by an increase in net positive charge. As is the case with inactivation and block of K+ channels, this is mediated by a large increase in Kon. These observations are consistent with the proposal that the conduction pathway of RyR contains negatively charged sites which will contribute to the ion handling properties of this channel.