A delayed rectifier current is modulated by the circadian pacemaker in Bulla.
Basal retinal neurons of the marine mollusc Bulla gouldiana continue to express a circadian modulation of their membrane conductance for at least two cycles in cell culture. Voltage-dependent currents of these pacemaker cells were recorded using the whole-cell perforated patch-clamp technique to characterize outward currents and investigate their putative circadian modulation. Three components of the outward potassium current were identified. A transient outward current (IA) was activated after depolarization from holding potentials greater than -30 mV, inactivated with a time constant of 50 ms, and partially blocked by 4-aminopyridine (1-5 mM). A Ca(2+)-dependent potassium current (IK(Ca)) was activated by depolarization to potentials more positive than -10 mV and was blocked by removing Ca2+ from the bath or by applying the Ca2+ channel blockers Cd2+ (0.1-0.2 mM) and Ni2+ (1-5 mM). A sustained Ca(2+)-independent current component including the delayed rectifier current (IK) was recorded at potentials positive to -20 mV in the absence of extracellular Na+ and Ca2+ and was partially blocked by tetraethylammonium chloride (TEA, 30mM). Whole-cell currents recorded before and after the projected dawn and normalized to the cell capacitance revealed a circadian modulation of the delayed rectifier current (IK). However, the IA and IK(Ca) currents were not affected by the circadian pacemaker.
Michel
S
S
Department of Biology, University of Virginia, Charlottesville 22903, USA. Smichel@rz.uni-leipzig.de
Manivannan
K
K
Zaritsky
J J
JJ
Block
G D
GD
D015761:4-Aminopyridine / Q000494:pharmacology; D000818:Animals; D001369:Axons / Q000502:physiology; D002118:Calcium / Q000378:metabolism; D002455:Cell Division / Q000187:drug effects; D002478:Cells, Cultured; D002940:Circadian Rhythm / Q000187:drug effects / Q000502:physiology*; D051668:Delayed Rectifier Potassium Channels; D015640:Ion Channel Gating / Q000187:drug effects; D008564:Membrane Potentials / Q000187:drug effects; D008670:Metals / Q000494:pharmacology; D008974:Mollusca / Q000166:cytology*; D009474:Neurons / Q000166:cytology / Q000187:drug effects / Q000502:physiology*; D018408:Patch-Clamp Techniques; D011188:Potassium / Q000378:metabolism; D015221:Potassium Channels / Q000187:drug effects / Q000502:physiology*; D024642:Potassium Channels, Voltage-Gated; D012160:Retina / Q000166:cytology / Q000502:physiology*; D012964:Sodium / Q000378:metabolism; D019789:Tetraethylammonium / Q000494:pharmacology
D051668:Delayed Rectifier Potassium Channels; D008670:Metals; D015221:Potassium Channels; D024642:Potassium Channels, Voltage-Gated; D019789:Tetraethylammonium; D012964:Sodium; D015761:4-Aminopyridine; D011188:Potassium; D002118:Calcium