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The Journal of Experimental Biology 205, 2705-2713 (2002)
© 2002 The Company of Biologists Limited

Effects of extracellular purines on ion transport across the integument of Hirudo medicinalis

Mikael Schnizler^*, Mirjam Buss and Wolfgang Clauss

Institut für Tierphysiologie der Justus-Liebig-Universität Giessen, Wartweg 95, D-35392 Giessen Germany

^* Author for correspondence (e-mail: Mikael.K.Schnizler{at}physzool.bio.uni-giessen.de)

Accepted 29 May 2002

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 µA 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.

Key words: leech, Hirudo medicinalis, Na⁺ transport, invertebrate, amiloride, cyclic AMP, ATP, adenosine, UTP

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