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Identification and characterisation of β‐adrenoceptors on intact equine peripheral blood lymphocytes with the radioligand (‐)‐[125I]‐iodocyanopindolol
Author(s) -
ABRAHAM G.,
BRODDE O.E.,
UNGEMACH F. R.
Publication year - 2001
Publication title -
equine veterinary journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.82
H-Index - 87
eISSN - 2042-3306
pISSN - 0425-1644
DOI - 10.2746/042516401776254862
Subject(s) - iodocyanopindolol , potency , agonist , antagonist , pindolol , chemistry , receptor , lymphocyte , radioligand , binding site , endocrinology , medicine , microbiology and biotechnology , intrinsic activity , biology , in vitro , biochemistry , immunology
Summary In this study, β‐adrenoceptors of intact equine lymphocytes were identified and subclassified by (‐)‐[ 125 I]‐iodocyanopindolol (ICYP) binding. ICYP binding to intact equine lymphocytes was rapid, saturable (maximal number of binding sites 320 ± 20 ICYP binding sites/cell, n = 12) and of high affinity (K D value for ICYP 14.4 ± 1.7 pmol/l, n = 12). Binding was stereospecific as shown by the 10 times greater potency of (‐)‐propranolol to inhibit binding than its (+)‐isomer. β‐adrenoceptor agonists inhibited ICYP binding with an order of potency: (‐)‐isoprenaline >(‐)‐adrenaline > (‐)‐noradrenaline; the same order of potency was obtained for agonist‐induced stimulation of lymphocyte cyclic AMPcontent. The selective β 2 ‐adrenoceptor antagonist ICI 118,551 was about 1000 times more potent in inhibiting ICYP binding than was the β 1 ‐selective adrenoceptor antagonist CGP 20712A. It is, therefore, concluded that in intact equine lymphocytes, ICYP labels a class of functional β‐adrenoceptors that belong predominantly (>90%) to the β 2 ‐adrenoceptor subtype; a small (<10%) β 1 ‐adrenoceptor component, however, cannot be ruled out completely. ICYP binding to equine lymphocytes might be a suitable model to study function and regulation of the β‐adrenoceptor system in the horse in vivo. The aim of this study was to characterise the β‐adrenoreceptor subtypes present on equine lymphocytes.