Thallous ion permeation through the cation-selective channel of the sarcoplasmic reticulum. Anomalous mole fraction dependence.

The thallous ion was found to permeate the cation-selective channel of rabbit sarcoplasmic reticulum and to block current through this channel when present in mixtures with other permeant ions. Channel conductance in pure thallium acetate saturates with increasing concentration, with a maximum limiting conductance of 60 pS. The conductance ratio GK/GTl at 1 M is 3.7, while the permeability ratio is near 0.4 over the concentration range 0.01 to 1 M. Thallium blockade in mixtures can be described by the equation of Neher (Neher, E. (1975) Biochim. Biophys. Acta 401, 540-544).