K(+) currents in cultured neurones from a polyclad flatworm.
Cells from the brain of the polyclad flatworm Notoplana atomata were dispersed and maintained in primary culture for up to 3 weeks. Whole-cell patch-clamp of presumed neurones revealed outwardly directed K(+) currents that comprised, in varying proportions, a rapidly activating (time constant tau =0.94+/-0.79 ms; N=15) and inactivating ( tau =26.1+/-1.9 ms; N=22) current and a second current that also activated rapidly ( tau =1.1+/-0.2 ms; N=9) (means +/- s.e.m.) but did not inactivate within 100 ms. Both current types activated over similar voltage ranges. Activation and steady-state inactivation overlap and are markedly rightward-shifted compared with most Shaker-like currents (half-activation of 16.9+/-1. 9 mV, N=7, half-inactivation of -35.4+/-3.0 mV, N=5). Recovery from inactivation was rapid (50+/-2.5 ms at -90 mV). Both currents were unaffected by tetraethylammonium (25 mmol l(-1)), whereas 4-aminopyridine (10 mmol l(-1)) selectively blocked the inactivating current. The rapidly inactivating current, like cloned K(+) channels from cnidarians and certain cloned K(+) channels from molluscs and the Kv3 family of vertebrate channels, differed from most A-type K(+) currents reported to date. These findings suggest that K(+) currents in Notoplana atomata play novel roles in shaping excitability properties.
Buckingham
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Bamfield Marine Station, Bamfield, British Columbia, Canada V0R 1B0. aspencer@bms.bc.ca
Spencer
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D015761:4-Aminopyridine / Q000494:pharmacology; D000818:Animals; D002478:Cells, Cultured; D004553:Electric Conductivity; D009420:Nervous System / Q000166:cytology; D009474:Neurons / Q000502:physiology*; D018408:Patch-Clamp Techniques; D010986:Platyhelminths / Q000502:physiology*; D015221:Potassium Channels / Q000502:physiology*
D015221:Potassium Channels; D015761:4-Aminopyridine