Characteristics of outward current induced by application of dopamine on a snail neuron.

1. A closer characterization of the potassium channel opened by the application of dopamine (DA) on an identified Helix pomatia neuron was attempted. The effect of K+ channel blockers (TEA and 4-AP) on the DA-induced current was examined. The results indicate that the channel opened by DA does not share the pharmacological properties of other snail neuron K-channels. 2. The I-V relation for IDA was successfully fitted by the Constant Field equation except below the reversal potential where the current was smaller than expected. The assumption that DA binding is voltage-sensitive is supported by the increment of the Hill coefficient with hyperpolarization (from nH approximately equal to 1 to nH approximately equal to 2). 3. The presence of the phosphodiesterase inhibitor IBMX does not affect the DA induced outward current. However, the assumption that the snail neurons' DA receptor belongs to the D2 class is in contrast to the antagonistic effects of ergot alkaloids which, in mammalian neurons, are competitive antagonists of D1 receptors. 4. The examination of the voltage-sensitivity of the blocking action of the ergot alkaloid (Bromoergocryptinine) revealed that it does not compete with DA for the same binding site as in mammalian D1 receptors.