A possible pacemaker mechanism in pars compacta neurons of the guinea-pig substantia nigra revealed by various ion channel blocking agents.
The membrane properties of pars compacta neurons in the in vitro guinea-pig substantia nigra have been studied in the presence of sodium, calcium and potassium channel blockers. The following properties, which have already been described for dopamine-containing substantia nigra zona compacta neurons were observed: high and low threshold calcium spikes; a calcium-activated potassium-mediated transient; inward rectification. Inward rectification was sensitive to caesium ions. An additional property was seen reminiscent of an "A" current, although resistant to 4-aminopyridine. It is suggested that this outward transient is in fact a calcium activated potassium conductance. Under certain conditions calcium-mediated rhythmic depolarizations were observed. It is suggested that at least two of the properties seen (outward rectification and low threshold calcium spike) could interact to provide the basis for a pacemaker mechanism in pars compacta neurons.
Harris
N C
NC
University Department of Pharmacology, Oxford, U.K.
Webb
C
C
Greenfield
S A
SA
D000200:Action Potentials / Q000187:drug effects; D000818:Animals; D002118:Calcium / Q000502:physiology; D002121:Calcium Channel Blockers / Q000494:pharmacology*; D015220:Calcium Channels / Q000187:drug effects / Q000502:physiology*; D005260:Female; D006168:Guinea Pigs; D066298:In Vitro Techniques; D008564:Membrane Potentials / Q000187:drug effects; D013378:Substantia Nigra / Q000187:drug effects / Q000502:physiology*
D002121:Calcium Channel Blockers; D015220:Calcium Channels; D002118:Calcium