Vagal inhibition in the antral region of guinea pig stomach.
The effects of vagal stimulation in the presence of a muscarinic antagonist were examined on three distinct rhythmically active cells located in guinea pig antrum. Vagal stimulation inhibited contractions of the circular muscle layer but did not change their rate of occurrence. With the use of intracellular recording techniques, these stimuli were found to initiate inhibitory junction potentials in the circular layer but produced smaller potential changes in driving and follower cells. Inhibition of the circular muscle layer involved two separate components. The dominant component was independent of changes in membrane potential and was abolished by nitro-L-arginine. After abolishing Ca(2+) entry into smooth muscle cells with a Ca(2+) antagonist, vagal stimulation continued to inhibit the residual contractions associated with each slow wave. When the cyclic changes in intracellular Ca(2+) concentration associated with each slow wave were measured, they were found to be unchanged by vagal stimulation. The observations suggest that vagal inhibition of stomach movements does not alter pacemaker activity in the stomach; rather, it results from a change in the sensitivity of smooth muscle contractile proteins to Ca(2+).
Department of Zoology, University of Melbourne, Parkville, Victoria Australia.
E J
EJ
Dickens
F R
FR
Edwards
G D
GD
Hirst
D000818:Animals; D002118:Calcium / Q000378:metabolism; D002121:Calcium Channel Blockers / Q000494:pharmacology; D004558:Electric Stimulation; D004594:Electrophysiology; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005260:Female; D006168:Guinea Pigs; D008297:Male; D009119:Muscle Contraction / Q000187:drug effects / Q000502:physiology; D009130:Muscle, Smooth / Q000294:innervation* / Q000502:physiology*; D009543:Nifedipine / Q000494:pharmacology; D019335:Nitroarginine / Q000494:pharmacology; D011706:Pyloric Antrum / Q000294:innervation* / Q000502:physiology*; D014630:Vagus Nerve / Q000502:physiology*
D002121:Calcium Channel Blockers; D004791:Enzyme Inhibitors; D019335:Nitroarginine; D009543:Nifedipine; D002118:Calcium