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Studies on a Capillary‐Rich Fraction Isolated from Brain: Histaminic Components and Characterization of the Histamine Receptors Linked to Adenylate Cyclase
Author(s) -
Karnushina I. L.,
Palacios J. M.,
Barbin G.,
Dux E.,
Joó F.,
Schwart J. C.
Publication year - 1980
Publication title -
journal of neurochemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.75
H-Index - 229
eISSN - 1471-4159
pISSN - 0022-3042
DOI - 10.1111/j.1471-4159.1980.tb09960.x
Subject(s) - histamine , receptor , histamine h2 receptor , cyclase , histamine receptor , histamine h1 receptor , chemistry , histamine n methyltransferase , adenylate kinase , cimetidine , medicine , endocrinology , biochemistry , biology , antagonist
A fraction enriched in capillaries has been prepared from the guinea pig cerebral cortex. The purity of this fraction was checked by light‐ and electron‐microscopic examination and by its high enrichment in alkaline phosphatase and γ‐glutamyl transpeptidase. In the capillary‐rich fraction, the endogenous level of histamine was 1.9%’of that measured in the initial hornogenate. The histamine‐synthesizing enzyme, I‐histidine decarboxylase, and the metabolizing enzyme, histamine‐N‐methyltransferase, were barely detectable. In addition, histamine elicits a twofold stimulation in the accumulation of cyclic AMP in this capillary fraction with an EC 50 of 5 γM. Agonists and antagonists of the two types of histamine receptors (H 1 and H 2 ) were used for the characterization of the receptors mediating this action: H 2 ‐receptor agonists were able to activate the adenylate cyclase with “relative potencies” similar to that found on typical H 2 ‐receptors, and cimetidine, a specific H 2 ‐receptor antagonist, competitively inhibited the response to histamine with a K 1 value reflecting its interaction with a single population of H 2 ‐receptors. On the contrary, data obtained with H 1 ‐receptor agonists and antagonists reflect their interaction with H 2 ‐receptors rather than H 1 ‐receptors. Thus H 2 ‐receptors are involved in the activation of adenylate cyclase of the capillary fraction.