Changes in the biochemical profiles of mid-cervically located adenosine A1 receptors after repeated theophylline administration in adult rats.
OBJECTIVE
Adenosine A1 receptors localized in the phrenic motoneurons (PMNs), where the axons of the descending bulbospinal respiratory make synaptic contacts, may be involved in theophylline-induced respiratory-related activity in rats. The objective of this study was to characterize the biochemical profiles of adenosine A1 receptors in 2 groups of rats: (a) naïve and (b) theophylline-treated (3-day oral administration).


METHODS
Biochemical binding characteristics of adenosine A1 receptors in the C3 to C5 (PMN) of adult rats were assessed in naïve (n = 6) and theophylline-treated animals (n = 6) using [3H]-DPCPX (10 pmol/L to 30 nmol/L), the specific adenosine A1 receptor antagonist in saturation-binding assays. Competition assays used theophylline as the competing ligand (20 mmol/L to 20 pmol/L), and protein concentration was determined with the Bradford assay using a range of standards (0.016-1.0 mg/mL).


RESULTS
In saturation-binding assays in naïve animals, the A1 receptor was characterized by a single binding site with Bmax and Kd values of 256.00 +/- 32.13 fmol/mg protein and 2.89 +/- 0.45 nmol/L, respectively. Analysis of the isotherm in theophylline-treated animals showed 1 site with Bmax and Kd values of 219.00 +/- 26.3 fmol/mg protein and 0.60 +/- 0.21 nmol/L, respectively, and a second site characterized by Bmax and Kd values of 492.6 +/- 3.15 fmol/mg protein and 14.09 +/- 2.06 nmol/L, respectively.


CONCLUSIONS
Theophylline administration revealed 2 binding sites on receptors (characterized by the specific adenosine A1 antagonist, [3H]-DPCPX) located in the vicinity of phrenic motoneurons (C3-C5). Alteration of the receptor profiles after theophylline may underlie the respiratory-related actions of the drug.
Saharan
Rubabe S
RS
Department of Anatomy and Cell Biology, Wayne State University, Detroit, Michigan 48202, USA.
Nantwi
Kwaku D
KD
D000284:Administration, Oral; D000818:Animals; D001665:Binding Sites; D001993:Bronchodilator Agents / Q000008:administration & dosage / Q000494:pharmacology*; D002574:Cervical Vertebrae; D004305:Dose-Response Relationship, Drug; D005260:Female; D009046:Motor Neurons / Q000378:metabolism*; D051381:Rats; D017207:Rats, Sprague-Dawley; D043682:Receptor, Adenosine A1 / Q000378:metabolism*; D012119:Respiration / Q000187:drug effects; D013806:Theophylline / Q000008:administration & dosage / Q000494:pharmacology*
D001993:Bronchodilator Agents; D043682:Receptor, Adenosine A1; D013806:Theophylline