title: Electrogenic cation transport across leech caecal epithelium.
abstract: Electrogenic cation transport across the caecal epithelium of the leech Hirudo medicinalis was investigated using modified Ussing chambers. Transepithelial resistance (RT) and potential difference (VT) were 61.0 +/- 3.5 omega.cm2 and -1.1 +/- 0.2 mV (n = 149), respectively, indicating that leech caecal epithelium is a "leaky" epithelium. Under control conditions short circuit current (ISC) and transepithelial Na+ transport rate (INa) averaged at 22.1 +/- 1.5 microA.cm-2 and 49.7 +/- 2.6 microA.cm-2, respectively. Mucosal application of amiloride (100 mumol.l-1) or benzamil (50 mumol.l-1) influenced neither ISC nor INa. The transport system in the apical membrane showed no pronounced cation selectivity and a linear dependence on mucosal Na+ concentration. Removal of mucosal Ca2+ increased ISC by about 50% due to an increase of transepithelial Na+ transport. Trivalent cations (La3+ and Tb3+, 1 mmol.l-1 both) added to the mucosal Ringer solution reduced INa by more than 40%. Serosal ouabain (1 mmol.l-1) almost halved ISC and INa while 0.1% (= 5.4 mmol.l-1) DNP decreased INa to 11.8 +/- 5.1% of initial values. Serosal addition of cAMP increased both ISC and INa whereas the neurotransmitters. FMRFamide, acetylcholine, GABA, L-dopa, serotonin and dopamine failed to show any effects; octopamine, glycine and L-glutamate reduced INa markedly. On the basis of these results we conclude that in leech caecal epithelium apical uptake of monovalent cations is mediated by non-selective cation conductances which are sensitive to extracellular Ca2+ but insensitive to amiloride. Basolaterally Na+ is extruded via ouabain-sensitive and -insensitive ATPases. cAMP activates Na+ transport across leech caecal epithelium, although the physiological stimulus for cAMP-production remains unknown.
authors.affiliation: Institute for Animal Physiology, Justus-Liebig-University Giessen, Germany.
authors.forename: H
authors.initials: H
authors.lastname: Milde
authors.forename: W
authors.initials: W
authors.lastname: Clauss
authors.forename: W M
authors.initials: WM
authors.lastname: Weber
mesh_terms: D000818:Animals; D001692:Biological Transport / Q000502:physiology; D002412:Cations / Q000378:metabolism*; D002432:Cecum / Q000378:metabolism*; D000242:Cyclic AMP / Q000494:pharmacology; D004140:Dinitrophenols / Q000494:pharmacology; D004594:Electrophysiology; D018698:Glutamic Acid / Q000494:pharmacology; D005998:Glycine / Q000494:pharmacology; D007473:Ion Channels / Q000502:physiology; D007865:Leeches / Q000378:metabolism*; D009655:Octopamine / Q000494:pharmacology; D010042:Ouabain / Q000494:pharmacology; D018408:Patch-Clamp Techniques; D000644:Quaternary Ammonium Compounds / Q000378:metabolism; D012964:Sodium / Q000378:metabolism / Q000494:pharmacology
chemical_list: D002412:Cations; D004140:Dinitrophenols; D007473:Ion Channels; D000644:Quaternary Ammonium Compounds; D009655:Octopamine; D018698:Glutamic Acid; D010042:Ouabain; D012964:Sodium; D000242:Cyclic AMP; C027917:tetramethylammonium; D005998:Glycine