AJP - Renal Physiology, Vol 260, Issue 6 839-F847, Copyright © 1991 by American Physiological Society
Effect of protamine on ion conductance of upper portion of descending limb of long-looped nephron from hamsters
S. Koyama, K. Yoshitomi and M. Imai
Department of Pharmacology, Jichi Medical School, Tochigi, Japan.
To estimate the contribution of paracellular shunt pathway to the
cation-selective permeability in the upper portion of the descending limb
of long-looped nephron (LDLu) of hamsters, we observed the effect of
protamine on salt-diffusion voltage (delta VT) and transmural resistance
(RT). delta VT generated on reduction of lumen NaCl concentration was
decreased from 12.0 +/- 1.4 to 7.3 +/- 1.2 mV when 100 micrograms/ml
protamine were added to the lumen. Although the effect of protamine
persisted after removal of the agent from the lumen, addition of 30 U/ml
heparin reversed the delta VT toward the control level. The effect of
protamine was dose dependent in the range from 3 to 1,000 micrograms/ml.
Protamine was without effect from the bath. Studies on single salt dilution
voltage revealed that 100 and 300 micrograms/ml protamine inhibited
relative Na+ to Cl- permeability from 4.03 +/- 0.38 to 2.14 +/- 0.21 and
from 3.75 +/- 0.37 to 1.36 +/- 0.09, respectively. Protamine markedly
decreased the apparent transference number for Na+ but slightly increased
the value for Cl-. Protamine also inhibited permeabilities for K+, Rb+, and
Li+ relative to Cl-, indicating that the inhibitory effect of protamine was
not confined to Na+ but was generalized to cations. Transmural cable
analysis showed that 100 micrograms/ml protamine increased RT from 14.0 +/-
1.1 to 19.3 +/- 1.2 omega.cm2, with the effect being reversed by 30 U/ml
heparin. Because the effect of protamine on RT was unaffected by ouabain in
the bath, changes in RT may mainly represent those of the paracellular
shunt resistance.(ABSTRACT TRUNCATED AT 250 WORDS)
