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Blockade by sigma site ligands of high voltage‐activated Ca 2+ channels in rat and mouse cultured hippocampal pyramidal neurones

Blockade by sigma site ligands of high voltage‐activated Ca 2+ channels in rat and mouse cultured... 1 The effects of a series of structurally‐dissimilar σ site ligands were examined on high voltage‐activated Ca2+ channel activity in two preparations of cultured hippocampal pyramidal neurones. 2 In mouse hippocampal neurones under whole‐cell voltage‐clamp, voltage‐activated Ca2+ channel currents carried by barium ions (IBa) were reduced with the rank order (IC50 values in μm): 1S,2R‐(–)‐cis‐N‐methyl‐N‐(2‐(3,4‐dichlorophenyl)ethyl)‐2‐(1‐pyrrolidinyl)cyclohexylamine (7.8) > rimcazole (13) > haloperidol (16)>ifenprodil (18)>opipramol (32)>carbetapentane (40)=1‐benzylspiro(1,2,3,4‐tetrahy‐dronaphthalene‐1,4‐piperidine) (42) >caramiphen (47) >dextromethorphan (73). At the highest concentrations tested, the compounds almost abolished IBa in the absence of any other pharmacological agent. 3 The current‐voltage characteristics of the whole‐cell IBa were unaffected by the test compounds. The drug‐induced block was rapid in onset and offset, with the exceptions of carbetapentane and caramiphen where full block was achieved only after two to three voltage‐activated currents and was associated with an apparent increase in the rate of inactivation of IBa 4 In rat hippocampal neurones loaded with the Ca2+‐sensitive dye Fura‐2, rises in intracellular free Ca2+ concentration evoked by transient exposure to 50 mM K+‐containing medium, either in the absence or in the presence of 10 μm nifedipine (to block L‐type high voltage‐activated Ca2+ channels), were also reversibly attenuated by the σ ligands. The rank order potencies for the compounds in these experimental paradigms were similar to that observed for blockade of IBa in the electrophysiological studies. 5 These results indicate that, at micromolar concentrations, the compounds tested block multiple subtypes of high voltage‐activated Ca2+ channels. These actions, which do not appear to be mediated by high‐affinity σ binding sites, may play a role in some of the functional effects previously described for the compounds. http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png British Journal of Pharmacology Wiley

Blockade by sigma site ligands of high voltage‐activated Ca 2+ channels in rat and mouse cultured hippocampal pyramidal neurones

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References (49)

Publisher
Wiley
Copyright
1995 British Pharmacological Society
ISSN
0007-1188
eISSN
1476-5381
DOI
10.1111/j.1476-5381.1995.tb15929.x
Publisher site
See Article on Publisher Site

Abstract

1 The effects of a series of structurally‐dissimilar σ site ligands were examined on high voltage‐activated Ca2+ channel activity in two preparations of cultured hippocampal pyramidal neurones. 2 In mouse hippocampal neurones under whole‐cell voltage‐clamp, voltage‐activated Ca2+ channel currents carried by barium ions (IBa) were reduced with the rank order (IC50 values in μm): 1S,2R‐(–)‐cis‐N‐methyl‐N‐(2‐(3,4‐dichlorophenyl)ethyl)‐2‐(1‐pyrrolidinyl)cyclohexylamine (7.8) > rimcazole (13) > haloperidol (16)>ifenprodil (18)>opipramol (32)>carbetapentane (40)=1‐benzylspiro(1,2,3,4‐tetrahy‐dronaphthalene‐1,4‐piperidine) (42) >caramiphen (47) >dextromethorphan (73). At the highest concentrations tested, the compounds almost abolished IBa in the absence of any other pharmacological agent. 3 The current‐voltage characteristics of the whole‐cell IBa were unaffected by the test compounds. The drug‐induced block was rapid in onset and offset, with the exceptions of carbetapentane and caramiphen where full block was achieved only after two to three voltage‐activated currents and was associated with an apparent increase in the rate of inactivation of IBa 4 In rat hippocampal neurones loaded with the Ca2+‐sensitive dye Fura‐2, rises in intracellular free Ca2+ concentration evoked by transient exposure to 50 mM K+‐containing medium, either in the absence or in the presence of 10 μm nifedipine (to block L‐type high voltage‐activated Ca2+ channels), were also reversibly attenuated by the σ ligands. The rank order potencies for the compounds in these experimental paradigms were similar to that observed for blockade of IBa in the electrophysiological studies. 5 These results indicate that, at micromolar concentrations, the compounds tested block multiple subtypes of high voltage‐activated Ca2+ channels. These actions, which do not appear to be mediated by high‐affinity σ binding sites, may play a role in some of the functional effects previously described for the compounds.

Journal

British Journal of PharmacologyWiley

Published: Dec 1, 1995

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