α1B adrenergic receptors in gonadotrophin‐releasing hormone neurones: relation to Transport‐P

• Published in: British journal of pharmacology Vol. 132; no. 1; pp. 336 - 344
• Main Authors: Al‐Damluji, S, Shen, W B, White, S, Barnard, E A
• Format: Journal Article
• Language: English
• Published: Oxford, UK Blackwell Publishing Ltd 01.01.2001; Nature Publishing
• Subjects: Adrenergic receptors, alpha; Biological and medical sciences; biological transport; Cell physiology; Cell receptors; Cell structures and functions; Fundamental and applied biological sciences. Psychology; hypothalamus; Membrane and intracellular transports; Molecular and cellular biology; Monoamines receptors (catecholamine, serotonine, histamine, acetylcholine); prazosin; Agonist; Biological transport; Peptide hormone; Rodentia; Central nervous system; Gonadotropin RH; α1-Adrenergic receptor; Molecular interaction; Catecholamine; Gene expression; In vitro; Hypothalamic hormone; Vertebrata; Peptidergic neuron; Mammalia; Alpha blocking agent; Mouse; Animal; Established cell line; Genetics; Norepinephrine; Antagonist; Hormone releasing factor; Brain (vertebrata)
• DOI: 10.1038/sj.bjp.0703781
• ISSN: 0007-1188

Peptidergic neurones accumulate amines via an unusual uptake process, designated Transport‐P. [3H]‐prazosin binds to α1 adrenoceptors on these cells and is displaceable by unlabelled prazosin in concentrations up to 10−7 M. However, at greater concentrations of prazosin, there is a paradoxical accumulation of [3H]‐prazosin which we have attributed to Transport‐P. Uptake of prazosin via Transport‐P is detectable at 10−10 M prazosin concentration, is linear up to 10−7 M and at greater concentrations becomes non‐linear. In contrast, in noradrenergic neurones, noradrenaline uptake is linear and saturates above 10−7 M. In noradrenergic neurones and in non‐neuronal cells, there is no uptake of prazosin in concentrations up to 10−6 M, suggesting that Transport‐P is a specialised function of peptidergic neurones. Using a mouse peptidergic (gonadotrophin‐releasing hormone, GnRH) neuronal cell line which possesses Transport‐P, we have studied the interaction of α1 adrenoceptors with Transport‐P. Polymerase chain reactions and DNA sequencing of the products demonstrated that only the α1B sub‐type of adrenoceptors is present in GnRH cells. In COS cells transfected with α1b adrenoceptor cDNA and in DDT1 MF‐2 cells which express native α1B adrenoceptors, [3H]‐prazosin was displaced by unlabelled prazosin in a normal equilibrium process, with no prazosin paradox in concentrations up to 10−6 M. In DDT1 MF‐2 cells, [3H]‐prazosin was displaced likewise by a series of α1 adrenergic agonists, none of which increased the binding of [3H]‐prazosin. Hence, the prazosin paradox is not due to some function of α1 adrenoceptors, such as internalization of ligand‐receptor complexes. In neurones which possess Transport‐P, transfection with α1b adrenoceptor cDNA resulted in over‐expression of α1B adrenoceptors, but the prazosin paradox was unaltered. Thus, α1 adrenoceptors and Transport‐P mediate distinct functions in peptidergic neurones. British Journal of Pharmacology (2001) 132, 336–344; doi:10.1038/sj.bjp.0703781