Identification and characterisation of beta-adrenoceptors on intact equine peripheral blood lymphocytes with the radioligand (-)-[125I]-iodocyanopindolol.
In this study, beta-adrenoceptors of intact equine lymphocytes were identified and subclassified by (-)-[125I]-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 (KD 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. Beta-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 AMP content. The selective beta2-adrenoceptor antagonist ICI 118,551 was about 1000 times more potent in inhibiting ICYP binding than was the beta1-selective adrenoceptor antagonist CGP 20712A. It is, therefore, concluded that in intact equine lymphocytes, ICYP labels a class of functional beta-adrenoceptors that belong predominantly (>90%) to the beta2-adrenoceptor subtype; a small (<10%) beta1-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 beta-adrenoceptor system in the horse in vivo. The aim of this study was to characterise the beta-adrenoreceptor subtypes present on equine lymphocytes.
Abraham
G
G
Institute of Pharmacology, Pharmacy and Toxicology, Faculty of Veterinary Medicine, University of Leipzig, Germany.
Broddet
O E
OE
Ungemach
F R
FR
D000319:Adrenergic beta-Antagonists; D000818:Animals; D001665:Binding Sites / Q000502:physiology; D000242:Cyclic AMP / Q000378:metabolism; D006736:Horses / Q000502:physiology*; D007457:Iodine Radioisotopes; D020120:Iodocyanopindolol; D007700:Kinetics; D008024:Ligands; D008214:Lymphocytes / Q000378:metabolism*; D011943:Receptors, Adrenergic, beta / Q000145:classification* / Q000302:isolation & purification*; D013237:Stereoisomerism
D000319:Adrenergic beta-Antagonists; D007457:Iodine Radioisotopes; D008024:Ligands; D011943:Receptors, Adrenergic, beta; D020120:Iodocyanopindolol; D000242:Cyclic AMP