Conductance and selectivity properties of a substate of the rabbit sarcoplasmic reticulum channel

In this paper I describe the occurrence and properties of a subconductance state of the cation-selective channel of the sarcoplasmic reticulum. The substate conductance is 60% of the major state conductance in every salt solution examined. When single channel conductance is plotted vs. ion concentration (for potassium or thallium salt solutions) the Michaelis-Menten constant is nearly the same for both conductance states, while the maximum conductance is reduced for the subconductance state. Both conductance states show anomalous conductance behavior in mixed potassium-thallium solutions that may be modeled in the same way. These results indicate that the ionic selectivity of the channel is the same for both open states.