Catecholamine stimulation of ion transport in the toad urinary bladder |
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Authors: | C L Thurman J T Higgins |
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Institution: | Department of Medicine, Medical College of Ohio, Toledo. |
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Abstract: | 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. |
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