title: Amiodarone and desethylamiodarone increase intrasynaptosomal free calcium through receptor mediated channel.
abstract: Long term amiodarone (AM) therapy has been associated with several side effects including neurotoxicity. Since AM alters Ca2+ regulated events, we have studied its effects on the compartmentation of free Ca2+ in the synaptosomes as an attempt to understand the mechanism of AM and its metabolite, desethylamiodarone (DEA)-induced neurotoxicity. Intact brain synaptosomes were prepared from male Sprague-Dawley rats. Both AM and DEA produced a concentration dependent increase in intrasynaptosomal free Ca2+ concentration ([Ca2]i) to micromolar levels. The increase in [Ca2]i was not transient and a steady rise was observed with time. Omission of Ca2+ from the external medium prevented the AM- and DEA-induced rise in [Ca2+]i suggesting that AM and DEA increased the intracellular [Ca2+]i due to increased influx of Ca2+ from external medium. AM- and DEA-induced increase in intrasynaptosomal [Ca2+]i was neither inhibited by a calcium channel blocker, verapamil, nor with a Na+ channel blocker, tetrodotoxin. However, the blockade of [Ca2+]i rise by AM and DEA was observed with MK-801, a receptor antagonist indicating that AM and DEA induced rise in [Ca2+]i is through receptor mediated channel. Both AM and DEA also inhibited N-methyl-D-aspartic acid (NMDA)-receptor binding in synaptic membranes in a concentration dependent manner, DEA being more effective, indicating that AM and DEA compete for the same site as that of NMDA and confirm the observation that these drugs increase intrasynaptosomal [Ca2+]i through receptor mediated channel. 45Ca accumulation into brain microsomes and mitochondria was significantly inhibited by AM and DEA, but without any effect on the Ca2+ release from these intracellular organelles.(ABSTRACT TRUNCATED AT 250 WORDS)
authors.affiliation: Department of Neurology, University of Mississippi Medical Center, Jackson 39216.
authors.forename: P R
authors.initials: PR
authors.lastname: Kodavanti
authors.forename: S N
authors.initials: SN
authors.lastname: Pentyala
authors.forename: P R
authors.initials: PR
authors.lastname: Yallapragada
authors.forename: D
authors.initials: D
authors.lastname: Desaiah
mesh_terms: D000638:Amiodarone / Q000031:analogs & derivatives* / Q000494:pharmacology*; D000818:Animals; D001665:Binding Sites; D002118:Calcium / Q000378:metabolism*; D015220:Calcium Channels / Q000187:drug effects* / Q000378:metabolism; D016291:Dizocilpine Maleate / Q000494:pharmacology; D008297:Male; D008861:Microsomes / Q000378:metabolism; D008928:Mitochondria / Q000378:metabolism; D051381:Rats; D011919:Rats, Inbred Strains; D016194:Receptors, N-Methyl-D-Aspartate / Q000378:metabolism; D015222:Sodium Channels / Q000187:drug effects; D013574:Synaptosomes / Q000187:drug effects / Q000378:metabolism*; D013779:Tetrodotoxin / Q000494:pharmacology; D014700:Verapamil / Q000494:pharmacology
chemical_list: D015220:Calcium Channels; D016194:Receptors, N-Methyl-D-Aspartate; D015222:Sodium Channels; D013779:Tetrodotoxin; D016291:Dizocilpine Maleate; D014700:Verapamil; C036116:desethylamiodarone; D000638:Amiodarone; D002118:Calcium