title: Calcium-mediated decrease of a voltage-dependent potassium current.
abstract: Elevated intracellular Ca++ concentration reduces the amplitude of an early, voltage-dependent K+ current (IA) in the Type B photoreceptor of Hermissenda crassicornis. Internal Ca++ is increased by activating a voltage and light-dependent Ca++ current present in these cells or by direct iontophoresis of Ca++ ions. Substitution of Ba++ for Ca++ or elimination of Ca++ from the sea water bathing the cells abolishes the reduction in IA during paired light and depolarizing voltage steps. The delayed K+ current (IB) in these cells is also reduced during paired light and voltage steps, but this decrease of IB is not affected by removal of extracellular Ca++. IB (but not IA), apparently much less dependent on intracellular Ca++ levels, is reduced by light alone. Ca++ iontophoresis also abolishes the light-dependent Na+ current, which recovers with a time course of minutes.
mesh_terms: D000818:Animals; D001369:Axons / Q000187:drug effects / Q000502:physiology*; D002118:Calcium / Q000494:pharmacology*; D007700:Kinetics; D008974:Mollusca / Q000502:physiology; D010786:Photoreceptor Cells / Q000187:drug effects / Q000502:physiology*; D011188:Potassium / Q000378:metabolism*; D013569:Synapses / Q000187:drug effects / Q000502:physiology*
chemical_list: D011188:Potassium; D002118:Calcium