Mercury (Hg2+) and zinc (Zn2+): two divalent cations with different actions on voltage-activated calcium channel currents.
1. We examined the actions of mercury (Hg2+) and zinc (Zn2+) on voltage-activated calcium channel currents of cultured rat dorsal root ganglion (DRG) neurons, using the whole-cell patch clamp technique. 2. Micromolar concentrations of both cations reduced voltage-activated calcium channel currents. Calcium channel currents elicited by voltage jumps from a holding potential of -80 to 0 mV (mainly L- and N-currents) were reduced by Hg2+ and Zn2+. The threshold concentration for Hg2+ effects was 0.1 microM and that for Zn2+ was 10 microM. Voltage-activated calcium channel currents were abolished (> 80%) with 5 microM Hg2+ or 200 microM Zn2+. The peak calcium current was reduced to 50% (IC50) by 1.1 microM Hg2+ or 69 microM Zn2+. While Zn2+ was much more effective in reducing the T-type calcium channel current--activated by jumping from -80 to -35 mV--Hg2+ showed some increased effectiveness in reducing this current. 3. The effects of both cations occurred rapidly and a steady state was reached within 1-3 min. While the action of Zn2+ was not dependent on an open channel state, Hg2+ effects depended partially on channel activation. 4. While both metal cations reduced the calcium channel currents over the whole voltage range, some charge screening effects were detected with Hg2+ and with higher concentrations (> 100 microM) of Zn2+. 5. As Zn2+ in the concentration range used had no influence on resting membrane currents, Hg2+ caused a clear inward current at concentrations > or 2 microM.(ABSTRACT TRUNCATED AT 250 WORDS)
Büsselberg
D
D
Heinrich-Heine Universität Düsseldorf, Germany.
Pekel
M
M
Michael
D
D
Platt
B
B
D000818:Animals; D000831:Animals, Newborn; D015220:Calcium Channels / Q000187:drug effects / Q000502:physiology*; D002413:Cations, Divalent / Q000494:pharmacology; D002478:Cells, Cultured; D004305:Dose-Response Relationship, Drug; D005727:Ganglia, Spinal / Q000502:physiology*; D007700:Kinetics; D008564:Membrane Potentials / Q000187:drug effects / Q000502:physiology; D008628:Mercury / Q000494:pharmacology*; D009474:Neurons / Q000187:drug effects / Q000502:physiology*; D018408:Patch-Clamp Techniques; D051381:Rats; D017208:Rats, Wistar; D013997:Time Factors; D015032:Zinc / Q000494:pharmacology*
D015220:Calcium Channels; D002413:Cations, Divalent; D008628:Mercury; D015032:Zinc