Ion transport across leech integument. I. Electrogenic Na+ transport and current fluctuation analysis of the apical Na+ channel.
The dorsal skin of the leech Hirudo medicinalis was used for electrophysiological measurements performed in Ussing chambers. The leech skin is a tight epithelium (transepithelial resistance = 10.5 +/- 0.5 k omega.cm-2) with an initial short-circuit current of 29.0 +/- 2.9 microA.cm-2. Removal of Na+ from the apical bath medium reduced short-circuit current about 55%. Ouabain (50 mumol.l-1) added to the basolateral solution, depressed the short-circuit current completely. The Na+ current saturated at a concentration of 90 mmol Na+.l-1 in the apical solution (KM = 11.2 +/- 1.8 mmol.l-1). Amiloride (100 mumol.l-1) on the apical side inhibited ca. 40% of the Na+ current and indicated the presence of Na+ channels. The dependence of Na+ current on the amiloride concentration followed Michaelis-Menten kinetics (Ki = 2.9 +/- 0.4 mumol.l-1). The amiloride analogue benzamil had a higher affinity to the Na+ channel (Ki = 0.7 +/- 0.2 mumol.l-1). Thus, Na+ channels in leech integument are less sensitive to amiloride than channels known from vertebrate epithelia. With 20 mmol Na+.l-1 in the mucosal solution the tissue showed an optimum amiloride-inhibitable current, and the amiloride-sensitive current under this condition was 86.8 +/- 2.3% of total short-circuit current. Higher Na+ concentrations lead to a decrease in amiloride-blockade short-circuit current. Stimulation of the tissue with cyclic adenosine monophosphate (100 mumol.l-1) and isobutylmethylxanthine (1 mmol.l-1) nearly doubled short-circuit current and increased amiloride-sensitive Na+ currents by 50%.(ABSTRACT TRUNCATED AT 250 WORDS)
Weber
W M
WM
Institut für Tierphysiologie, Justus-Liebig-Universität Giessen, Germany.
Dannenmaier
B
B
Clauss
W
W
D000584:Amiloride / Q000031:analogs & derivatives / Q000493:pharmacokinetics / Q000494:pharmacology; D000818:Animals; D017136:Ion Transport / Q000187:drug effects; D007700:Kinetics; D007865:Leeches / Q000378:metabolism*; D012867:Skin / Q000378:metabolism; D012964:Sodium / Q000378:metabolism; D015222:Sodium Channels / Q000187:drug effects / Q000378:metabolism
D015222:Sodium Channels; C013407:benzamil; D000584:Amiloride; D012964:Sodium