The effects of electrical stimulation, adenosine and adenosine-5'-triphosphate (ATP) on mouse rectal muscle

The effects of electrical field stimulation and of purine compounds, adenosine and adenosine-5'-triphosphate (ATP) were examined on the mouse isolated rectum. Electrical field stimulation induced frequency-dependent contractions of mouse rectal muscles which were potentiated by physostigmine and inhibited by atropine or tetrodotoxin. Contractile amplitude at 37 degrees C was significantly (P less than 0.05) greater than at 25 degrees C, but the degree of potentiation by physostigmine was significantly (P less than 0.05) greater at 25 degrees C. ATP (1.6 x 10(-4)-1.28 x 10(-3) M) and adenosine (1.8 x 10(-4)-1.48 x 10(-3) M) inhibited in concentration-related fashion contractile responses induced by KCl (1.34 x 10(-2) M-1.07 x 10(-1) M) by acetylcholine (2.2 x 10(-7) M-1.4 x 10(-5) M) and by CaCl2 in high KCl (120 mM)-CaCl2-free Tyrode solution. Theophylline and quinidine ('purinoceptor' antagonists) antagonized ACH contractile effects and so could not be satisfactorily employed in the characterization of the purine receptors in the mouse rectum. It may be concluded from this study that in the mouse rectum, acetylcholine is an excitatory neurotransmitter and that there is a non-adrenergic, non-cholinergic inhibitory neuromuscular transmission in this tissue. Further, ATP and adenosine have been demonstrated to cause relaxation in this tissue by possibly a post-synaptic mechanism involving inhibition of Ca2+ influx into the depolarized muscle.