Ionic currents in identified swimmeret motor neurones of the crayfish Pacifastacus leniusculus

Ionic currents from freshly isolated and identified swimmeret motor neurones were characterized using a whole-cell patch-clamp technique. Two outward currents could be distinguished. A transient outward current was elicited by delivering depolarizing voltage steps from a holding potential of -80 mV. This current was inactivated by holding the cells at a potential of -40 mV and was also blocked completely by 4-aminopyridine. A second current had a sustained time course and continued to be activated at a holding potential of -40 mV. This current was partially blocked by tetraethylammonium. These outward currents resembled two previously described potassium currents: the K+ A-current and the delayed K+ rectifier current respectively. Two inward currents were also detected. A fast transient current was blocked by tetrodotoxin and inactivated at holding potential of -40 mV, suggesting that this is an inward Na+ current. A second inward current had a sustained time course and was affected neither by tetrodotoxin nor by holding the cell at a potential of -40 mV. This current was substantially enhanced by the addition of Ba2+ to the bath or when equimolar Ba2+ replaced Ca2+ as the charge carrier. Furthermore, this current was significantly suppressed by nifedipine. All these points suggest that this is an L-type Ca2+ current. Bath application of nifedipine into an isolated swimmeret preparation affected both the frequency of the swimmeret rhythm and the duration of power-stroke activity, suggesting an important role for the inward Ca2+ current in maintaining a regular swimmeret rhythmic activity in crayfish.