Dopamine modulation of calcium currents in pyloric neurons of the lobster stomatogastric ganglion

We examined the dopamine (DA) modulation of calcium currents (I-Ca) that could contribute to the plasticity of the pyloric network in the lobster stomatogastric ganglion. Pyloric somata were voltage-clamped under conditions designed to block voltage-gated Na+, K+, and H currents. Depolarizing steps from - 60 mV generated voltage-dependent, inward currents that appeared to originate in electrotonically distal, imperfectly clamped regions of the cell. These currents were blocked by Cd2+ and enhanced by Ba2+ but unaffected by Ni2+. Dopamine enhanced the peak I-Ca in the pyloric constrictor (PY), lateral pyloric (LP), and inferior cardiac (IC) neurons and reduced peak I-Ca in the ventricular dilator (VD), pyloric dilator (PD), and anterior burster (AB) neurons. All of these effects, except for the AB, are consistent with DA's excitation or inhibition of firing in the pyloric neurons. Enhancement of I-Ca in PY and LP neurons and reduction of I-Ca in VD and PD neurons are also consistent with DA-induced synaptic strength changes via modulation of presynaptic I-Ca. However, the reduction of I-Ca in AB suggests that DA's enhancement of AB transmitter release is not directly mediated through presynaptic I-Ca. I-Ca in PY and PD neurons was more sensitive to nifedipine block than in AB neurons. In addition, nifedipine blocked DA's effects on I-Ca in the PY and PD neurons but not in the AB neuron. Thus the contribution of specific calcium channel subtypes carrying the total I-Ca may vary between pyloric neuron classes, and DA may act on different calcium channel subtypes in the different pyloric neurons.