title: Modulation of postjunctional cholinergic sensitivity of rat diaphragm muscle by cyclic adenosine monophosphate.
abstract: Addition of 2.5 mM cyclic adenosine monophosphate (cAMP) to the solution bathing a rat diaphragm muscle alters the magnitude of depolarization responses to iontophoretic pulses of acetylcholine (ACh) at neuromuscular endplates. Alterations are repeatable with small variability on a given preparation for initial and repeat experiments on both hemidiaphragms, but are different on each preparation. Five min after addition of the nucleotide solution, increases (potentiations) of up to 30% above control levels and decreases (attenuations) to 50% below control levels are observed. The effects on sensitivity to ACh of dibutyryl cAMP (1.25 mM), monobutyryl cAMP (0.25 mM), and cAMP (2.5 mM) in Ca++ -free solution are a function of whether the experiment is an initial one on that preparation or a repeat experiment after 10 or more minutes of perfusion flow. In all three cases, initial exposure attenuates sensitivity (means at 5 min: --30, --10, and --20%, respectively) and repeat exposure potentiates sensitivity (mean: 20% at 5 min, 15% at 5 min, and 10% at 2 min respectively). A concentration of dibutyryl cAMP (0.25 mM) which is without effect on sensitivity alone, produces a large, transient potentiation (mean: 45% at 1 min) in conjunction with 0.5 mM theophylline. A decrease in the rate of desensitization is observed during exposure to 0.25 mM cAMP. The results are interpreted in terms of a physiological mechanism whereby receptor activity at the postjunctional membrane is modulated by cAMP formed from prejunctionally released ATP.
mesh_terms: D000109:Acetylcholine / Q000494:pharmacology*; D000818:Animals; D003994:Bucladesine / Q000494:pharmacology; D000242:Cyclic AMP / Q000031:analogs & derivatives / Q000494:pharmacology*; D006152:Cyclic GMP / Q000031:analogs & derivatives / Q000494:pharmacology; D003964:Diaphragm; D008564:Membrane Potentials / Q000187:drug effects*; D009130:Muscle, Smooth / Q000187:drug effects*; D009469:Neuromuscular Junction / Q000187:drug effects*; D051381:Rats; D013806:Theophylline / Q000494:pharmacology
chemical_list: D003994:Bucladesine; D013806:Theophylline; D000242:Cyclic AMP; D006152:Cyclic GMP; D000109:Acetylcholine