Effects of extracellular purines on ion transport across the integument of Hirudo medicinalis.
Little is known about the long-term regulation of epithelial ion transport in invertebrates and the specific mediators involved. For some years, we have been investigating the short-term regulation of transepithelial ion transport across the dorsal integument of the leech Hirudo medicinalis, and we have established a model of Na+ uptake. In the present study, we investigated the effect of long-term acclimation on transintegumental ion transport by adapting leeches to high-salinity conditions. We dissected segments of dorsal integument and measured ion currents in Ussing chamber experiments. Electrophysiological variables, such as transepithelial potential (V(T)) and short-circuit-current (I(sc)), were profoundly affected by adaptation to high-salinity conditions. The total transepithelial Na+ current (I(Na)) decreased from 7.66+/-0.82 to 4.6+/-0.54 microA cm(-2) in preparations adapted to high salinity. The involvement of epithelial Na+ channels was determined as current inhibition (I(ami)) by apical application of amiloride; Na+ channels were equally active in control epithelia and epithelia from leeches adapted to high salinity. Removal of Ca2+ from the apical solutions, which is believed to reduce intracellular Ca2+ concentrations, equalized transepithelial variables between high-salt-adapted integuments and control integuments. Extracellular purines regulate transepithelial Cl- secretion and Na+ absorption. In a variety of tissues we tested ATP and adenosine for their effects on epithelial transport. Examination of integuments from pondwater- and high-salinity-adapted leeches revealed different sensitivities for these purines. Apical and basolateral application of ATP both stimulated transepithelial Na+ uptake and I(ami). Adenosine upregulated non-Na+ currents and acted from the basolateral side only. Apical Ca2+-free conditions attenuated these effects of purines on transepithelial currents. Extracellular UTP had no effect on ion transport.
Schnizler
Mikael
M
Institut für Tierphysiologie der Justus-Liebig-Universität Giessen, Wartweg 95, D-35392 Giessen Germany. Mikael.K.Schnizler@physzool.bio.uni-giessen.de
Buss
Mirjam
M
Clauss
Wolfgang
W
D000241:Adenosine / Q000494:pharmacology; D000255:Adenosine Triphosphate / Q000494:pharmacology; D000818:Animals; D002118:Calcium / Q000378:metabolism; D004848:Epithelium / Q000187:drug effects / Q000378:metabolism; D017136:Ion Transport / Q000187:drug effects; D007865:Leeches / Q000187:drug effects / Q000378:metabolism*; D011687:Purines / Q000494:pharmacology; D018047:Receptors, Purinergic P1 / Q000378:metabolism; D018048:Receptors, Purinergic P2 / Q000378:metabolism; D012964:Sodium / Q000378:metabolism; D014544:Uridine Triphosphate / Q000494:pharmacology
D011687:Purines; D018047:Receptors, Purinergic P1; D018048:Receptors, Purinergic P2; D000255:Adenosine Triphosphate; D012964:Sodium; D000241:Adenosine; D002118:Calcium; D014544:Uridine Triphosphate