Lead and zinc block a voltage-activated calcium channel of Aplysia neurons

Dietrich Busselberg, M. L. Evans, H. Rahmann, D. O. Carpenter

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Abstract

The effects of Pb2+ and Zn2+ on the peak of the voltage-activated calcium current of Aplysia neurons were examined. Calcium currents were reversibly blocked by Pb2+ at concentrations that did not significantly affect potassium and sodium currents and by Zn2+ at concentrations associated with a delay and reduction of peak sodium and potassium currents. The block by both was concentration dependent, and percentage blockade was reduced in elevated Ca2+. The threshold Pb2+ concentration for blockade in 20 mM Ca artificial sea water (ASW) was ~1 μM, whereas for Zn2+ it was 2 mM. The Hill coefficient for Pb2+ action was near 1.0 under all conditions, whereas for Zn2+ it was 1.4-1.6. With addition of Pb2+, the voltage at which peak calcium current was generated shifted to hyperpolarized voltages, an effect similar to that caused by reduction of Ca2+ concentration in the absence of Pb2+. Zn2+ shifted the voltage at which peak current was generated in a depolarizing direction. Pb2+ did not significantly change inactivation but shifted the voltage dependence of activation to hyperpolarized voltages in a dose-dependent manner. Zn2+ shifted both activation and inactivation in a depolarizing direction in a dose-dependent fashion. The blockade of calcium currents by Pb2+ but not Zn2+ was highly voltage dependent and increased with depolarization. Our results suggest that Pb2+ is a specific, potent, competitive, and reversible blocker of calcium currents. These observations are consistent with a competition by Pb2+ with Ca2+ at a binding site within the calcium channel. In contrast, the blockade of calcium currents by Zn2+ is probably through actions at fixed charge sites external to the channel.

Original languageEnglish
Pages (from-to)786-795
Number of pages10
JournalJournal of Neurophysiology
Volume65
Issue number4
Publication statusPublished - 1991
Externally publishedYes

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ASJC Scopus subject areas

  • Physiology
  • Neuroscience(all)

Cite this

Busselberg, D., Evans, M. L., Rahmann, H., & Carpenter, D. O. (1991). Lead and zinc block a voltage-activated calcium channel of Aplysia neurons. Journal of Neurophysiology, 65(4), 786-795.