Characteristics of the anion channel in the sino-atrial node cell of the rabbit.

1. The anion permeability of the sino-atrial node cell membranes was determined by substituting various anions for Cl and observing the resultant transient changes in membrane potential. The permeability sequence was found to be in the following order: thiocyanate greater than NO3 greater than I Br greater than Cl greater than acetate. 2. The membrane resistance in Cl solution was compared with that in various anion solutions by the voltage-clamp method. The conductance sequence for the sino-atrial node cell membrane was observed to be the same as the permeability sequence. 3 The potential generated by the Na-K pump was partly short-circuited in normal bathing solution, and thus the pump could be responsible in part for the generation of the sin-atrial node resting membrane potential. 4 When Cl was replaced by acetate, a less permeable ion, the inward-going rectification disappeared. Thus, the inward-going rectification might be due partly to a time- and voltage-dependent Cl current.