ISSN:
1432-1912
Keywords:
Amiodarone
;
Desethylamiodarone
;
Free Ca2+
;
Fura-2
;
Synaptosomes
;
45Ca-uptake
;
Inositol phosphates
Source:
Springer Online Journal Archives 1860-2000
Topics:
Medicine
Notes:
Summary 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. Also, both these drugs did not interfere with inositol 1,4,5-trisphosphate induced Ca2+ release from microsomes even at 10 μM concentration. These results clearly indicate that both AM and DEA increase intrasynaptosomal [Ca2+]i by an action on receptor mediated channel in plasma membrane, but not due to the release of Ca2+ from intracellular storage sites. This initial rise in [Ca2+]i, together with other changes in Ca2+ homeostasis, might be responsible for AM and DEA-induced neurotoxicity.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/BF00165739
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