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Antimalarial drugs inhibit calcium-dependent backward swimming and calcium currents in Paramecium calkinsi
Authors:S R Barry  J Bernal
Institution:(1) Department of Physical Medicine & Rehabilitation, University Hospital Rm 1D204, University of Michigan, 48109-0042 Ann Arbor, MI, USA;(2) Departamento de Fisiologia y Farmacologia, Universidad Autonoma de Aguascalientes, 20100 Aguascalientes, Ags, CP, Mexico;(3) Marine Biological Laboratory, 02543 Woods Hole, MA, USA;(4) Present address: Dept. of Biological Sciences, Mount Holyoke College, 01075 South Hadley, MA, USA
Abstract:The antimalarial drugs, quinacrine, chloroquine, quinine, primaquine, and mefloquine, share structural similarities with W-7, a compound that inhibits calcium-dependent backward swimming and calcium currents in Paramecium. Therefore, we tested whether antimalarial drugs also inhibit backward swimming and calcium currents in P. calkinsi. When the Paramecium is depolarized in high potassium medium, voltage-dependent calcium channels in the ciliary membrane open causing the cell to swim backward for 30 to 70 s. Application of calcium channel inhibitors, such as W-7, reduce the duration of backward swimming. In 0.05 mM calcium, quinacrine, mefloquine, quinine, chloroquine, primaquine and W-7 all reduced the duration of backward swimming. These effects were seen in sodium-containing and sodium-free high potassium solutions as well as sodium-free depolarizing solutions containing potassium channel blockers. In these low calcium solutions, backward swimming was inhibited by 50% at concentrations ranging from 100 nM to 30 mgrM. At higher calcium concentrations (1 mM or 15 mM), the effects of the antimalarials and W-7 were reduced. The effects of quinacrine and W-7 were tested directly on calcium currents using the two microelectrode voltage clamp technique. In 15 mM calcium, 100 mgrM quinacrine and 100 mgrM W-7 reduced the peak calcium current by 51% and 42%, respectively. Thus, antimalarial drugs reduce calcium currents in Paramecium calkinsi.
Keywords:Paramecium  Antimalarial drugs  Calcium currents  Quinacrine  Calcium channel blockers
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