CHARACTERIZATION OF HISTAMINE RECEPTORS COUPLED TO TRITIUM - CYCLIC-AMP ACCUMULATION IN A VESICULAR PREPARATION OF GUINEA PIG CORTEX.
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Title
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CHARACTERIZATION OF HISTAMINE RECEPTORS COUPLED TO TRITIUM - CYCLIC-AMP ACCUMULATION IN A VESICULAR PREPARATION OF GUINEA PIG CORTEX.
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Identifier
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AAI8601680
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identifier
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8601680
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Creator
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NEWTON, MAUREEN VALERIE.
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Contributor
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Lindsay B. Hough
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Date
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1985
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Language
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English
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Publisher
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City University of New York.
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Subject
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Biology, Neuroscience
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Abstract
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The histamine-stimulated accumulation of ('3)H-cyclic AMP (formed by prelabeling with ('3)H-adenine) was characterized pharmacologically in a vesicular preparation of guinea pig cortex to identify the receptors mediating this response.;Systematic variation of the preincubation time, vessel size, buffer composition, and ('3)H-adenine labeling time significantly influenced both the basal and histamine-stimulated ('3)H-cyclic AMP levels, and showed that individual prelabeling of aliquots in Kreb's-Ringer bicarbonate (15 mM) buffer yielded the most reproducible histamine responses.;Characterization of this histamine response showed that the H(,2)-antagonist cimetidine maximally blocked 80% of the response, whereas only 45% of the response could be inhibited by H(,1)-antagonists. A combination of H(,1)- and H(,2)-antagonists completely abolished the response. These and other findings show that both H(,1)- and H(,2)-receptors mediate the response, but 25% of the response may require concomitant activation of both receptors.;A role for adenosine as a mediator of the histamine response was investigated. Adenosine deaminase (2.5 U/ml) decreased the basal ('3)H-cyclic AMP levels; under these conditions the histamine response was completely abolished by cimetidine (300 uM), whereas mepyramine (3 uM) reduced the response by 30%. Thus, the H(,1)-response may be partially dependent upon endogenous adenosine. A combination of adenosine deaminase and the calcium chelator EGTA (2 mM) completely eliminated the H(,1)-component.;A "metactoid" model was developed to account for the H(,2)-, H(,1)-, and adenosine components of the histamine response. The model hypothesizes that 55% of the response is due to direct H(,2)-receptor stimulation, 25% is dependent on the metactoid sensitization of the H(,2)-response by H(,1)-receptors, and 20% is due to an analogous sensitization of adenosine responses by H(,1)-receptors. Affinity constants for both types of HA receptor antagonists, determined from fitting the above data to this model, were in agreement with literature values for these drugs.;These findings resolve previous controversies regarding the identity of the receptors mediating histamine-stimulated accumulation of cyclic AMP in brain. Furthermore, the vesicular preparation and metactoid model developed presently may be of benefit in other studies of neurotransmitter control of cyclic AMP dynamics.
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Type
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dissertation
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Source
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PQT Legacy CUNY.xlsx
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degree
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Ph.D.
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Program
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Biomedical Sciences
