PKC-dependent reduction of the acetylcholine-evoked inward Na current in Aplysia D-neurons: effect of injected PKC and PKC activators.

The effect of elevated PKC activity on the membrane depolarization (D-response) evoked by extracellular ACh, applied on the soma of Aplysia neurons, was studied. Intracellularly injected PKC and certain PKC activators were used to elevate PKC activity. ACh-induced current was measured in voltage clamp. The neurons were treated extracellularly with the PKC activators: PDAc, SC-10, R-59949, (-)-ILV; or with purified PKC injected into the neuron through the recording electrode. PKC injection and treatment with any of the PKC activators caused a similar reduction of the ACh-induced inward Na current response (corresponding to D-response), while the non-activating alpha-PDD had no effect. The results provide evidence that a PKC-dependent reduction of receptor responses also exists in this kind of Aplysia neurons. Furthermore, they show that the reduction of ACh response is indeed due to PKC activation (and not to a direct action of the phorbol ester).