Permeability characteristics of the red blood cell membrane to
okadaic acid and calyculin a.
Namboodiripad, Anil N., and Michael L. Jennings.
Department of Physiology and Biophysics, University of Texas
Medical Branch, Galveston, Texas 77555-0641
APStracts 2:0300C, 1995.
The rates of transport of the protein phosphatase inhibitors okadaic
acid and calyculin A through rabbit erythrocyte membranes have been
estimated by measuring protein phosphatase 2A (PP2A) activity in
lysates. High concentrations of okadaic acid (100 nM) cause rapid
(t1/2 nearly equal to 10 minutes) inhibition of PP2A. However, the
t1/2 for okadaic acid influx is much longer because the concentration
is much higher than the IC50. The estimated t1/2 is over one hour at
37 degrees C and over 4 hours at 25 degrees C. The effect of low
extracellular pH indicates that the undissociated acid is the
permeant species. It takes hours to reverse the effect of okadaic
acid, because the efflux must proceed through several half-times
before the concentration is below the IC50 for PP2A. In contrast to
okadaic acid, the permeation of calyculin A is too fast to measure at
25 degrees C. Our results indicate that okadaic acid entry into red
blood cells is slower than is generally believed; it is crucial to
consider concentration, temperature, pH, and time of exposure to
okadaic acid to interpret the effects of this agent on intact cells.
Received 23 June 1995; accepted in final form 9 August 1995.
APS Manuscript Number C368-5.
Article publication pending Am. J. Physiol. (Cell Physiology).
ISSN 1080-4757 Copyright 1995 The American Physiological Society.
Published in APStracts on 24 August 1995.