Voltage-activated calcium currents in identified neurons from a hydrozoan jellyfish, Polyorchis penicillatus.
Calcium currents were studied in isolated "swim motor neurons" from the jellyfish Polyorchis penicillatus, using the tight-seal, whole-cell, voltage-clamp technique. Two high-voltage-activated (HVA) currents were observed. The transient current, HVA-t, activated rapidly (time to peak, 4 msec), inactivated with two time constants (26 msec, 187 msec) in a positive voltage range (Vi = -23 mV), and was larger when carried by calcium than by barium ions. The sustained current, HVA-s, inactivated slowly or not at all, even at very positive voltages and had the same amplitude whether carried by Ca2+ or Ba2+. It is likely that the two HVA current components arise from distinct channel populations, because the ionic selectivity of calcium channels is not known to depend on their inactivation kinetics. A third current appeared to activate at very positive voltages, and at a slower rate than did HVA-t. It is likely to be an artifact of inhomogeneous space clamping. A low-voltage-activated, cadmium-insensitive calcium current may also be present. Calcium currents in this primitive, multicellular animal have properties similar to calcium currents in other phyla; however, they do not fit neatly into the "T, N, L" classification scheme of vertebrate calcium currents.
Przysiezniak
J
J
Department of Zoology, University of Alberta, Edmonton, Canada.
Spencer
A N
AN
D000818:Animals; D002104:Cadmium / Q000494:pharmacology; D002118:Calcium / Q000502:physiology*; D002413:Cations, Divalent / Q000378:metabolism; D004594:Electrophysiology; D006706:Homeostasis; D009474:Neurons / Q000502:physiology*; D009543:Nifedipine / Q000494:pharmacology; D037401:Scyphozoa; D013997:Time Factors; D014700:Verapamil / Q000494:pharmacology
D002413:Cations, Divalent; D002104:Cadmium; D014700:Verapamil; D009543:Nifedipine; D002118:Calcium