Na/k/2cl-cotransport, na/h-exchange and cell volume in ferret red
cells.
Mairb[umlaut]aurl, Heimo, and Christiane Herth.
Department of Sports Medicine, University of Heidelberg,
Hospitalstr.3, D - 69115 Heidelberg, Germany
APStracts 3:0194C, 1996.
Ferrets have high Na and low K erythrocytes (113 and 5.4 mmol/l cell
water) due to the lack of Na/K-pumps. Since ferret red cells have a
high capacity for Na/K/2Cl-cotransport, the present study was
undertaken to evaluate cell volume related changes in cotransport
activity and its role in volume regulation. Upon cell shrinkage
Na/K/2Cl-cotransport is about 2-fold activated. A large bumetanide
-insensitive Na-uptake component is found in shrunken erythrocytes
that has not been described yet. Its inhibition by amiloride (IC50 =
12[mu]M) and the Na-dependency of amiloride-sensitive extracellular
pH-changes measured in cells suspended in hypertonic, unbuffered
media indicate that this flux represents Na/H-exchange. Shrinkage
activation of both transporters follows a time lag of about 3 min, it
also requires normal levels of ATP. ATP-depletion inhibits Na/K/2Cl
-cotransport even at normal cell volume. Both transporters are
partially inhibited by the protein kinase inhibitors staurosporine
and K252a, activators of PK-A and PK-C do not affect transport.
Okadaic acid inhibition of protein phosphatases activates Na/K/2Cl
-cotransport to its maximal activity (the same after shrinkage),
shrinkage and okadaic acid activation are not additive. In contrast,
okadaic acid activates Na/H-exchange even in shrunken cells. These
results indicate that cell shrinkage activates Na/K/2Cl-cotransport
and Na/H-exchange probably by phosphorylation processes.
Received 11 September 1995; accepted in final form 24 May 1996.
APS Manuscript Number C552-5.
Article publication pending Am. J. Physiol. (Cell Physiology).
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 28 June 96