Effects of okadaic acid and intracellular cl-on na+,k+,cl-
cotransport.
Altamirano, Anibal A., Gerda E. Breitwieser, and John M. Russell.
Department of Physiology, Medical College of Pennsylvania and
Hahnemann University, Philadelphia, PA 19129, and, *Department of
Physiology, Johns Hopkins University School of Medicine, Baltimore,
MD 21205, and, Marine Biological Laboratory, Woods Hole, MA 02543
APStracts 2:0162C, 1995.
The Na+,K+,Cl- cotransporter of the squid giant axon requires ATP and
is inhibited by intracellular Cl- in a concentration-dependent manner
([Cl-]i >/=200 mM completely inhibits the cotransporter). In the
present study we address the question of whether inhibition of
cotransport by intracellular Cl- is due to a Cl-i-induced increase of
protein phosphatase activity. Intracellular dialysis was used to
apply the phosphatase inhibitor, okadaic acid (OKA), under conditions
of [Cl-]i = 0 or 150 or 300 mM while measuring cotransporter-mediated
unidirectional Cl- influx into axons. At 0 mM [Cl-]i, the application
of 250 nM OKA had no effect on the cotransport-mediated Cl- influx
when axons were dialyzed with the normal [ATP]i (4 mM). Reduction of
[ATP] to 50 NM resulted in a significant decrease of the bumetanide
-sensitive Cl- influx which could be partially reversed by OKA
treatment. Similarly, in ATP-limited axons with a [Cl-]i of 150 mM,
cotransporter influx was partially stimulated by treatment with OKA.
However, axons dialyzed with 300 mM [Cl-]i ([ATP]i = 50 NM) had no
measurable cotransport influx nor was subsequent treatment with OKA
able to induce a cotransport-mediated Cl- influx. We conclude that
the inhibition of cotransport caused by intracellular Cl- is not the
result of an increase in the OKA-sensitive protein phosphatase
activity.
Received 17 October 1994; accepted in final form 4 April 1995.
APS Manuscript Number C616-4.
Article publication pending Am. J. Physiol. (Cell Physiology).
ISSN 1080-4757 Copyright 1995 The American Physiological Society.
Published in APStracts on 19 April 1995.