alpha(2)-adrenoceptors inhibit antidiuretic hormone-stimulated Na+ absorption across tight epithelia (Rana esculenta)

Citation
Cn. Gudme et al., alpha(2)-adrenoceptors inhibit antidiuretic hormone-stimulated Na+ absorption across tight epithelia (Rana esculenta), PFLUG ARCH, 442(3), 2001, pp. 346-352
Citations number
27
Language
INGLESE
art.tipo
Article
Categorie Soggetti
Physiology
Journal title
PFLUGERS ARCHIV-EUROPEAN JOURNAL OF PHYSIOLOGY
ISSN journal
0031-6768 → ACNP
Volume
442
Issue
3
Year of publication
2001
Pages
346 - 352
Database
ISI
SICI code
0031-6768(200106)442:3<346:AIAHNA>2.0.ZU;2-Q
Abstract
In the present study we examined the effect of alpha -adrenergic regulation of active transepithelial Na+ absorption across the isolated frog skin epi thelium. alpha -Adrenergic stimulation was achieved by addition of the adre nergic agonist noradrenaline in the presence of the beta -adrenergic blocke r propranolol. alpha -Adrenergic stimulation inhibited basal as well as ant idiuretic hormone (ADH)-stimulated Na+ transport. The ADH-induced increase in Na+ transport was accompanied by a membrane depolarisation due to an inc rease in the apical Na+ permeability. The subsequent application of noradre naline inhibited the Na+ transport and repolarised the membrane potential, suggesting that alpha -adrenergic stimulation had reduced the apical Na+ pe rmeability. The inhibition was abolished by the alpha (2)-adrenergic antago nist yohimbine whereas it was insensitive to the alpha (1)-adrenergic antag onist prazosin. alpha -adrenergic stimulation had no effect on the cytosoli c free [Ca2+] ([Ca2+](i)). Incubation of the epithelium in the presence of ADH increased the cellular adenosine 3',5'-cyclic monophosphate (cAMP) cont ent, an increase which was abolished by a-adrenergic activation. The effect of alpha -adrenergic stimulation on cAMP production was abolished by the a lpha (2)-adrenergic antagonist yohimbine. We conclude that the noradrenalin e-induced inhibition of the ADH-stimulated Na+ absorption and cAMP content is mediated by activation of alpha (2)-adrenoceptors. The data further indi cate that the principal cells of the epithelium do not express al-adrenocep tors. The noradrenaline-induced inhibition of the ADH-stimulated Na+ transp ort was concentration dependent, with 0.24 +/-0.03 muM eliciting a half-max imal response. This alpha (2)-adrenergic-mediated down-regulation of Na+ ab sorption is achieved at a concentration of noradrenaline which begins to ac tivate the NaCl secretion via the skin glands. The alpha (2)-adrenoceptors therefore appear to have considerable physiological importance.