Summation of membrane current conductance responses as evidence for independent ionophore populations

1. The ramped voltage clamp technique was utilized to measure the maximum conductance changes in response to the application of pairs of agonists.2. Two types of cells were investigated. (a) depolarized by ACh and 5-HT. (b) hyperpolarized by ACh and glutamate.3. Membrane conductance was increased to the same ionic species by each pair of agonists in the cells investigated.4. Membrane conductance increases to simultaneous application of two agonists were equal to the arithmetic sum of membrane conductance changes to the sequential addition of the same doses of agonists, even when responses were maximal.5. There was no competition between the pairs of agonists for a common ionophore population