Inhibition of 5-HT3 receptor-mediated ion current by divalent metal cations in NCB-20 neuroblastoma cells.
1. The effect of micromolar concentrations of divalent metal cations on ion current activated by 5-hydroxytryptamine (5-HT) was investigated in NCB-20 neuroblastoma cells by the use of the whole-cell, patch-clamp technique. 2. Ion current activated by 5-HT in these cells was mimicked by 5-HT3 receptor agonists, blocked by nanomolar concentrations of selective 5-HT3 receptor antagonists and reversed polarity at approximately 0 mV. These properties indicate that this current is carried primarily if not exclusively by the nonspecific cation channel activated by the 5-HT3 receptor. 3. The Group IIb metal cations Cd2+ and Zn2+ and the Group Ib cation Cu2+ inhibited 5-HT-activated current with inhibition increasing in a concentration-dependent manner over micromolar concentrations of the ions. The order of potency of the ions for inhibiting 5-HT-activated current was Zn2+ (IC50 = 20 microM) greater than or equal to Cu2+ (IC50 = 25 microM) greater than Cd2+ (IC50 = 75 microM) at -50 mV. The other divalent metal cations tested (Ba2+, Co2+, Mg2+, Mn2+, and Ni2+) produced little or no inhibition of 5-HT-activated current at concentrations up to 200 microM. 4. Inhibition of 5-HT-activated current by Cd2+ and Zn2+ was dependent on membrane potential with the Kd increasing e-fold per 72 and 52 mV, respectively. Inhibition by Cu2+ was much less voltage dependent with the Kd increasing e-fold per 233 mV. 5. Inhibition by all three cations decreased with increasing concentration of agonist over a range of 5-HT concentrations from 1 to 10 microM.(ABSTRACT TRUNCATED AT 250 WORDS)
Lovinger
D M
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Unit of Synaptic Pharmacology, National Institute on Alcohol Abuse and Alcoholism, Rockville, Maryland 20852.
D000818:Animals; D002413:Cations, Divalent / Q000494:pharmacology*; D007473:Ion Channels / Q000187:drug effects*; D008564:Membrane Potentials / Q000502:physiology; D051379:Mice; D009423:Nervous System Neoplasms / Q000378:metabolism*; D009447:Neuroblastoma / Q000378:metabolism*; D011985:Receptors, Serotonin / Q000187:drug effects / Q000502:physiology*; D012702:Serotonin Antagonists; D014407:Tumor Cells, Cultured / Q000187:drug effects / Q000378:metabolism
D002413:Cations, Divalent; D007473:Ion Channels; D011985:Receptors, Serotonin; D012702:Serotonin Antagonists