Synaptosomal free [Ca2+] is reduced by clonidine and dynorphin A-(1-13) and increased by idazoxan.
Intrasynaptosomal free calcium concentrations measured in rat cortical synaptosomes using the calcium sensitive fluorescent dye quin 2, were found to be 0.107-0.122 microM (n = 33). Stimulation of alpha 2-adrenoceptors or kappa-opiate receptors with clonidine (0.1-100 microM) or dynorphin A fragment (1-13) (0.2-5.0 microM) respectively, produced a dose dependent reduction in the intrasynaptosomal free calcium concentration. The alpha 2-adrenoceptor mediated reduction produced by clonidine (100 microM) was antagonised by the selective alpha 2-antagonist idazoxan (RX781094) (200 microM). Dynorphin A-(1-13) (1 microM) caused a reduction which was antagonised by a high (20 microM) but not low (2.0 microM) concentration of naloxone. We conclude that unlike the mu- and delta-opiate receptor, stimulation of alpha 2-adrenoceptors or kappa-opiate receptors elicits changes in intrasynaptosomal free calcium concentration which are independent of the voltage sensitive calcium channel. This does not preclude the possibility that the alpha 2-adrenoceptor and kappa-opiate receptor also have an effect at the voltage sensitive calcium channel.
D000317:Adrenergic alpha-Antagonists / Q000494:pharmacology*; D000818:Animals; D001921:Brain / Q000378:metabolism; D002118:Calcium / Q000378:metabolism*; D003000:Clonidine / Q000494:pharmacology*; D004146:Dioxanes / Q000494:pharmacology*; D004147:Dioxins / Q000494:pharmacology*; D004399:Dynorphins / Q000494:pharmacology*; D004743:Enkephalin, Leucine / Q000031:analogs & derivatives / Q000494:pharmacology; D016308:Enkephalin, Leucine-2-Alanine; D019329:Idazoxan; D066298:In Vitro Techniques; D008297:Male; D009020:Morphine / Q000494:pharmacology; D009270:Naloxone / Q000494:pharmacology; D010446:Peptide Fragments / Q000494:pharmacology*; D051381:Rats; D011919:Rats, Inbred Strains; D013574:Synaptosomes / Q000187:drug effects / Q000378:metabolism*
D000317:Adrenergic alpha-Antagonists; D004146:Dioxanes; D004147:Dioxins; D010446:Peptide Fragments; D009270:Naloxone; D004743:Enkephalin, Leucine; D016308:Enkephalin, Leucine-2-Alanine; C026843:dynorphin (1-13); D004399:Dynorphins; D009020:Morphine; D003000:Clonidine; D002118:Calcium; D019329:Idazoxan