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A Delayed Rectifier Current Is Modulated by the Circadian Pacemaker in Bulla

Department of Biology, NSF Center for Biological Timing, University of Virginia, Charlottesville, VA 22903; Institut für Zoologie, Universität Leipzig, Talstrasse 33, 04103 Leipzig, Germany; Smichel{at}rz.uni-leipzig.de

Kandiah Manivannan

Department of Biology, NSF Center for Biological Timing, University of Virginia, Charlottesville, VA 22903; Department of Chemistry and Physics, Southeastern Louisiana University, Hammond, LA 70402

Joshua J. Zaritsky

Department of Biology, NSF Center for Biological Timing, University of Virginia, Charlottesville, VA 22903; Department of Molecular and Cellular Physiology, Stanford School of Medicine, Stanford, CA 94305-5426

Gene D. Block

Department of Biology, NSF Center for Biological Timing, University of Virginia, Charlottesville, VA 22903

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 (I_A) 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 Ca2+-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 Ca2+-independent current component including the delayed rectifier current (I_K) 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 (I_K). However, the I_A and IK(Ca) currents were not affected by the circadian pacemaker.

Key Words: potassium conductance • mollusc • retinal neurons • perforated-patch • Ca2+-dependent current • transient current

Journal of Biological Rhythms, Vol. 14, No. 2, 141-150 (1999)
DOI: 10.1177/074873099129000533


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