title: Regulation of electrogenic Na+ transport across leech skin.
abstract: The dorsal integument of the medical leech Hirudo medicinalis exhibits a marked amiloride-sensitive Na+ absorption. With 20 mM Na+ in the apical solution, the transepithelial short-circuit current (Isc) was approximately 40% higher than with 115 mM Na+, whereas the transepithelial potential (VT) with 20 mM Na+ was -35.7 +/- 4.5 and -20.6 +/- 2.6 mV with 115 mM Na+. Amiloride (100 microM) inhibition at 20 mM apical Na+ was also significantly larger than with 115 mM Na+ in the solution. Benzamil (100 microM) showed additional inhibition after amiloride. Large transient overshooting currents occurred only when 115 mM Na+ was added after some minutes of Na(+)-free apical solution. Addition of adenosine 3',5'-cyclic monophosphate (cAMP) to the serosal side in the presence of 115 mM apical Na+ nearly doubled Isc. This cAMP effect was reduced to only 20% in the presence of 20 mM Na+. Guanosine 3',5'-cyclic monophosphate (cGMP) slightly increased Isc, whereas ATP showed biphasic potency. Removal of calcium from the apical side resulted in a large stimulation of amiloride-sensitive Isc only in the presence of 115 mM Na+. When currents were activated with cAMP, a deprivation of Ca2+ modestly reduced the amiloride-sensitive Isc. The Na+ channel of leech integument was found highly selective for Na+ over other monovalent cations. The permeability ratio for Na+ over K+ was approximately 30:1; the selectivity relationship for the investigated cations was Na+ > Li+ > NH4+ > K+ approximately Cs+ approximately Rb+.
authors.affiliation: Institut für Tierphysiologie, Justus-Liebig-Universität Giessen, Germany.
authors.forename: W M
authors.initials: WM
authors.lastname: Weber
authors.forename: U
authors.initials: U
authors.lastname: Blank
authors.forename: W
authors.initials: W
authors.lastname: Clauss
mesh_terms: D000584:Amiloride / Q000031:analogs & derivatives / Q000494:pharmacology; D000818:Animals; D002118:Calcium / Q000378:metabolism; D000242:Cyclic AMP / Q000494:pharmacology; D006152:Cyclic GMP / Q000031:analogs & derivatives / Q000494:pharmacology; D004563:Electrochemistry; D006706:Homeostasis; D066298:In Vitro Techniques; D017136:Ion Transport; D007700:Kinetics; D007865:Leeches / Q000378:metabolism*; D000644:Quaternary Ammonium Compounds / Q000494:pharmacology; D012867:Skin / Q000187:drug effects / Q000378:metabolism*; D012964:Sodium / Q000378:metabolism*; D015222:Sodium Channels / Q000187:drug effects / Q000378:metabolism
chemical_list: D000644:Quaternary Ammonium Compounds; D015222:Sodium Channels; C013407:benzamil; C016276:8-bromocyclic GMP; D000584:Amiloride; D012964:Sodium; D000242:Cyclic AMP; C027917:tetramethylammonium; D006152:Cyclic GMP; D002118:Calcium