Catecholamine stimulation of ion transport in the toad urinary bladder.
We have observed that serosal catecholamines increase the amplitude of the short-circuit current (Isc) in the toad urinary bladder by as much as 450%. Chemical sympathectomy with 10(-6) M 6-hydroxydopamine and the sympathomimetic effects of 10(-5) M tyramine indicate a reservoir of amines in the serosal stroma of the tissue. The urinary epithelium from the toad responds to six adrenoceptor agonists: (-)-epinephrine, (-)-norepinephrine, (-)-phenylephrine, clonidine, methoxamine and oxymetazoline. The alpha 2-adrenoceptor agonist clonidine is most potent for stimulating Isc. Some agonists were found to diminish Isc. Apparently this is related to a simultaneous increase in the transepithelial flux of both chloride and sodium. The Isc response to the catecholamines is also inhibited by several adrenoceptor antagonists. The alpha 2-adrenoceptor antagonist yohimbine is more effective than the alpha 1-antagonist prazosin for blocking the stimulation of epithelial transport. As a result of these studies, we have tentatively classified the serosal adrenoceptor of the toad urinary bladder as alpha 2.
D000316:Adrenergic alpha-Agonists / Q000494:pharmacology; D000317:Adrenergic alpha-Antagonists / Q000494:pharmacology; D000584:Amiloride / Q000494:pharmacology; D000818:Animals; D001692:Biological Transport / Q000187:drug effects; D002024:Bufo marinus; D004837:Epinephrine / Q000494:pharmacology*; D066298:In Vitro Techniques; D007700:Kinetics; D008564:Membrane Potentials / Q000187:drug effects; D009638:Norepinephrine / Q000494:pharmacology*; D001743:Urinary Bladder / Q000187:drug effects / Q000502:physiology*
D000316:Adrenergic alpha-Agonists; D000317:Adrenergic alpha-Antagonists; D000584:Amiloride; D009638:Norepinephrine; D004837:Epinephrine