On the Effect of Ionophoretically Applied Dopamine on Salivary Gland Cells of Nauphoeta Cinerea

1. Responses to ionophoretically applied dopamine ('ionophoretic responses') have been recorded with an intracellular micro-electrode from acini of isolated salivary glands of the cockroach, Nauphoeta cinerea. They resembled responses to nerve stimulation ('neural responses') but they usually decayed more slowly and were sometimes more rapid in onset. 2. As already described for neural resonses, ionophoretic responses (i) included a secondary phase of depolarization (although more rarely than neural responses), (ii) increased in duration with increased amplitude and (iii) when small, added superlinearly. These features therefore reflect post-synaptic processes. By contrast, tachyphylaxis was much more marked for neural responses and is therefore mainly of presynaptic origin. 3. Ionophoretic and neural responses were affected similarly by increase in temperature. The times-to-peak of both decreased with values for Q10 of about 3. 4. The differences between the onset and decay of ionophoretic and neural responses can probably be explained by the inherently different conditions of application of the agonist. The similarities therfore provide further support for dopamine as the neurotransmitter.