Regulation of Agonist-Receptor Binding by G Proteins and Divalent Cations in Spermatozoa Solubilized A1 Adenosine Receptors

1998 ◽  
Vol 63 (3) ◽  
pp. 183-190 ◽  
Author(s):  
Alba Minelli ◽  
Cinzia Allegrucci ◽  
Roberto Rosati ◽  
Isabella Mezzasoma
Keyword(s):  
G Proteins ◽  
Receptor Binding ◽  
Adenosine Receptors ◽  
Divalent Cations ◽  
A1 Adenosine Receptors

scholarly journals Interactions of purified bovine brain A1-adenosine receptors with G-proteins. Reciprocal modulation of agonist and antagonist binding

1991 ◽  
Vol 275 (3) ◽  
pp. 651-656 ◽  
Author(s):  
M Freissmuth ◽  
E Selzer ◽  
W Schütz
Keyword(s):  
G Proteins ◽  
Adenosine Receptor ◽  
Adenosine Receptors ◽  
Bovine Brain ◽  
Detergent Solution ◽  
Maximal Effect ◽  
A1 Adenosine Receptor ◽  
Molar Excess ◽  
A1 Adenosine Receptors ◽  
Antagonist Binding

The bovine brain A1-adenosine receptor was purified 8000-fold by affinity chromatography on xanthine-amine-congener (XAC)-Sepharose. Addition of a 120-fold molar excess of a purified bovine brain G-protein preparation (Go,i a mixture of Go and Gi, containing predominantly Go) decreases the Bmax of the binding of the antagonist radioligand [3H]XAC to the receptor. This decrease is observed not only after insertion into phospholipid vesicles but also in detergent solution, and is reversed by GTP analogues. In the presence of Go,i, about 20 and 40% of the receptors display guanine-nucleotide-sensitive high-affinity binding of the agonist radioligand (-)-N6-3-([125I]iodo-4-hydroxyphenylisopropyl)adenosine after reconstitution into lipid vesicles and in detergent solution, respectively. The ability of Go,i to enhance agonist binding and decrease antagonist binding is concentration-dependent, with a half-maximal effect occurring at approximately 10-fold molar excess of G-proteins over A1-adenosine receptors. In the presence of the receptor, the rate of guanosine 5′-[gamma-[35S]thio]triphosphate (GTP[35S]) binding to Go,i is accelerated. This rate is further enhanced if the receptor is activated by the agonist (-)(R)-N6-phenylisopropyladenosine, whereas the antagonist XAC decreases the association rate of GTP[35S] to levels observed in the absence of receptor. These results show (1) that detergent removal is not a prerequisite for the observation of coupling between the A1-adenosine receptor and Go,i, and (2) that the regulatory effect of G-proteins on antagonist binding to the A1-adenosine receptor can be reconstituted by using purified components.

Cellular mechanisms underlying adenosine actions on cholinergic transmission in enteric neurons

1996 ◽  
Vol 271 (1) ◽  
pp. C264-C275 ◽  
Author(s):  
C. Barajas-Lopez ◽  
A. L. Peres ◽  
R. Espinosa-Luna
Keyword(s):  
G Proteins ◽  
Adenosine Receptors ◽  
Kinase Inhibitor ◽  
Protein Complexes ◽  
Calcium Currents ◽  
Enteric Neurons ◽  
Dependent Manner ◽  
Cholinergic Transmission ◽  
Cellular Mechanisms ◽  
A1 Adenosine Receptors

Whole cell recordings were used to investigate the effects of adenosine and several of its analogues on voltage-activated calcium currents (VACC) of myenteric and submucosal neurons. Electrophysiological and pharmacological properties of the soma VACC recorded in myenteric neurons indicate that they are carried through N-type calcium channels, similar to those of the submucosal neurons and to those of the calcium conductance that mediates acetylcholine release at the submucosal ganglia. Adenosinergic compounds inhibited, in a concentration-response and in a voltage-dependent manner, VACC in neurons from both enteric plexuses. The pharmacological profile of the receptors that mediate this effect was similar to that of the receptors involved in presynaptic inhibition in enteric neurons and likely of the A1 subtype. The effects of 2-chloroadenosine (CADO) on VACC were prevented by pretreatment with pertussis toxin (PTX), became irreversible with guanosine 5'-O-(3-thiotriphosphate) (inside the pipette), and were abolished with N-ethylmaleimide (NEM; known to uncouple receptors from G protein complexes). Intracellular recordings were used to further evaluate presynaptic effects of adenosine at the submucosal plexus. Adenosinergic compounds reduced the amplitude of fast excitatory postsynaptic potentials (EPSPs) by acting at nerve terminals. This effect was insensitive to PTX and staurosporine (a protein kinase inhibitor) but was abolished by NEM. CADO effects on EPSPs were not reversed by increasing the extracellular calcium concentration. In conclusion, activation of A1 adenosine receptors inhibits VACC via PTX-sensitive G proteins in myenteric and submucosal neurons. Reduction of cholinergic transmission also involves A1 adenosine receptors and appears to involve the activation of PTX-insensitive G proteins.

scholarly journals Role of the Prenyl Group on the G Protein γ Subunit in Coupling Trimeric G Proteins to A1 Adenosine Receptors

1996 ◽  
Vol 271 (31) ◽  
pp. 18588-18595 ◽  
Author(s):  
Hiroshi Yasuda ◽  
Margaret A. Lindorfer ◽  
Karen A. Woodfork ◽  
Julia E. Fletcher ◽  
James C. Garrison
Keyword(s):  
G Protein ◽  
G Proteins ◽  
Adenosine Receptors ◽  
Γ Subunit ◽  
A1 Adenosine Receptors

scholarly journals Species differences in structure-activity relationships of adenosine agonists and xanthine antagonists at brain A1 adenosine receptors

FEBS Letters ◽  
1986 ◽  
Vol 209 (1) ◽  
pp. 122-128 ◽  
Author(s):  
Dieter Ukena ◽  
Kenneth A. Jacobson ◽  
William L. Padgett ◽  
Cristina Ayala ◽  
Mah T. Shamim ◽  
...  
Keyword(s):  
Adenosine Receptors ◽  
Species Differences ◽  
Structure Activity Relationships ◽  
Structure Activity ◽  
Adenosine Agonists ◽  
A1 Adenosine Receptors

scholarly journals Immunolocalization of A1 Adenosine Receptors in Mammalian Spermatozoa

2000 ◽  
Vol 48 (9) ◽  
pp. 1163-1171 ◽  
Author(s):  
A. Minelli ◽  
C. Allegrucci ◽  
P. Piomboni ◽  
R. Mannucci ◽  
C. Lluis ◽  
...  
Keyword(s):  
Adenosine Receptors ◽  
A1 Adenosine Receptors ◽  
Mammalian Spermatozoa
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