Calcium sites in MSH stimulation of xenopus melanophores: studies with photoreactive alpha-MSH.
Mol Cell Endocrinol
; 26(3): 327-9, 1982 May.
Article
em En
| MEDLINE
| ID: mdl-6281100
ABSTRACT
Photo-affinity labelling of MSH receptors on tail-fin melanophores of Xenopus tadpoles with p-azidophenylalanine 13-alpha-MSH (Pap13)-alpha-MSH) or p-azidophenylacetyl-serine1-alpha-MSH ([Apac-Ser1]-alpha-MSH) resulted in a long-lasting stimulation of the melanophores which cannot be reversed despite continuous washing. The generation of this irreversible response is inhibited when photo-affinity labelling is performed in a Ca2+-free medium or in the presence of Ca2+ antagonists. The irreversible stimulation produced in normal medium is completely reversed upon removal of Ca2+ , but is not affected by Ca2+ antagonists or melatonin. Re-addition of Ca2+ after temporary removal restores to irreversible stimulation, even in the presence of Ca2+ antagonists or melatonin. This proves that covalent alpha-MSH-receptor complexes remain fully functional despite temporary deprivation of ca2+. Racemized alpha-MSH, which binds 'tightly' to the receptor and produces a long-lasting effect, is removed from the receptor in Ca2+-free medium, but not by Ca2+ antagonists or melatonin. These results confirm earlier results showing that at least 2 Ca2+ sites are involved in alpha-MSH action, one associated with MSH-receptor binding and the other with the subsequent generation of the effect. The dual role of Ca2+ is not the result of EGTA present; it is specific (Mg2+ has no effect) and is identical for the two different photoreactive alpha-MSH derivatives.
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Coleções:
01-internacional
Base de dados:
MEDLINE
Assunto principal:
Azidas
/
Receptores do Hormônio Hipofisário
/
Alfa-MSH
/
Cálcio
/
Receptores de Superfície Celular
/
Melanóforos
Limite:
Animals
Idioma:
En
Revista:
Mol Cell Endocrinol
Ano de publicação:
1982
Tipo de documento:
Article