title: Voltage control of Ca²⁺ permeation through N-type calcium (Ca(V)2.2) channels.
abstract: Voltage-gated calcium (Ca(V)) channels deliver Ca(2+) to trigger cellular functions ranging from cardiac muscle contraction to neurotransmitter release. The mechanism by which these channels select for Ca(2+) over other cations is thought to involve multiple Ca(2+)-binding sites within the pore. Although the Ca(2+) affinity and cation preference of these sites have been extensively investigated, the effect of voltage on these sites has not received the same attention. We used a neuronal preparation enriched for N-type calcium (Ca(V)2.2) channels to investigate the effect of voltage on Ca(2+) flux. We found that the EC50 for Ca(2+) permeation increases from 13 mM at 0 mV to 240 mM at 60 mV, indicating that, during permeation, Ca(2+) ions sense the electric field. These data were nicely reproduced using a three-binding-site step model. Using roscovitine to slow Ca(V)2.2 channel deactivation, we extended these measurements to voltages <0 mV. Permeation was minimally affected at these hyperpolarized voltages, as was predicted by the model. As an independent test of voltage effects on permeation, we examined the Ca(2+)-Ba(2+) anomalous mole fraction (MF) effect, which was both concentration and voltage dependent. However, the Ca(2+)-Ba(2+) anomalous MF data could not be reproduced unless we added a fourth site to our model. Thus, Ca(2+) permeation through Ca(V)2.2 channels may require at least four Ca(2+)-binding sites. Finally, our results suggest that the high affinity of Ca(2+) for the channel helps to enhance Ca(2+) influx at depolarized voltages relative to other ions (e.g., Ba(2+) or Na(+)), whereas the absence of voltage effects at negative potentials prevents Ca(2+) from becoming a channel blocker. Both effects are needed to maximize Ca(2+) influx over the voltages spanned by action potentials.
authors.affiliation: Department of Biology and Health Sciences, Pace University, New York, NY 10038 Department of Physiology, Tulane University Health Sciences Center, New Orleans, LA 70112.
authors.forename: Zafir
authors.initials: Z
authors.lastname: Buraei
authors.affiliation: Department of Physiology, Tulane University Health Sciences Center, New Orleans, LA 70112.
authors.forename: Haoya
authors.initials: H
authors.lastname: Liang
authors.affiliation: Department of Physiology, Tulane University Health Sciences Center, New Orleans, LA 70112 The Baker Laboratory of Pharmacology, Department of Pharmacology, Kirksville College of Osteopathic Medicine, A.T. Still University of Health Sciences, Kirksville, MO 63501 kelmslie@atsu.edu.
authors.forename: Keith S
authors.initials: KS
authors.lastname: Elmslie
mesh_terms: D000818:Animals; D001464:Barium / Q000494:pharmacology; D001665:Binding Sites; D002118:Calcium / Q000378:metabolism*; D002121:Calcium Channel Blockers / Q000494:pharmacology; D020864:Calcium Channels, N-Type / Q000737:chemistry / Q000378:metabolism*; D002478:Cells, Cultured; D017136:Ion Transport; D008564:Membrane Potentials; D009474:Neurons / Q000187:drug effects / Q000378:metabolism / Q000502:physiology; D011687:Purines / Q000494:pharmacology; D011892:Rana catesbeiana; D000077546:Roscovitine
chemical_list: D002121:Calcium Channel Blockers; D020864:Calcium Channels, N-Type; D011687:Purines; D000077546:Roscovitine; D001464:Barium; D002118:Calcium
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