The action of neurotransmitter hormones and analogues and cyclic nucleotides and theophylline on electrolyte transport by the excretory duct of the rabbit mandibular gland.

The effects of autonomic drugs on electrolyte transport by the main duct of the rabbit mandibular gland were studied in vitro. Acetylcholine, in concentrations as low as 10(-10) M, reduced nett Na+ reabsorption and partially depolarized the transepithelial potential difference (P.D.); the effects were blocked by atropine. Acetylcholine was relatively ineffective applied from the luminal rather than the interstitial surface of the duct. Noradrenaline and isoproterenol produced similar effects to acetylcholine but the minimum effective concentrations were much higher (10(-7) M and 10(-3) M, respectively). It was concluded that the duct cells possessed specific muscarinic receptors on the basal cell membrane but that adrenergic receptors, particularly beta receptors, were either scanty or lacking altogether. Theophylline (10(-5) M) could mimic the effects of the autonomic drugs and produced a dramatic potentiation of the action of acetylcholine. Both cAMP and cGMP (4 times 10(-5) M) mimicked the acetylcholine response but cAMP was only effective when applied to the luminal cell membrane. It is proposed that cAMP is the intracellular mediator of the acetylcholine response and that it produces some of its effects by acting on an enzyme system close to the apical cell membrane.