Sensitivity of transient outward rectification to ion channel blocking agents in guinea-pig substantia nigra pars compacta neurones in vitro.

The sensitivity of a transient outward rectifier in guinea-pig substantia nigra pars compacta (SNC) neurones in vitro was tested to a variety of ion channel blocking agents. This rectification was not blocked by TEA (10 mM), 4-aminopyridine (4-AP) (5 mM), apamin (0.2-1 microM) or Cd2+ ions (200 microM). Cs+ ions (5 mM) blocked the inward 'anomalous' rectifier but had no effect on the transient outward rectification. However, replacing Ca2+ ions in the bath perfusate by Ba2+ blocked the transient outward but not the inward rectifier. It is suggested that an atypical barium-sensitive conductance is responsible for the transient outward rectification of these neurones.