AJP - Regulatory, Integrative and Comparative Physiology, Vol 268, Issue 3 605-R613, Copyright © 1995 by American Physiological Society
Regulation of electrogenic Na+ transport across leech skin
W. M. Weber, U. Blank and W. Clauss
Institut fur Tierphysiologie, Justus-Liebig-Universitat Giessen, Germany.
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+.
