AJP - Cell Physiology, Vol 252, Issue 6 C618-C622, Copyright © 1987 by American Physiological Society
Human platelet diffusional water permeability measured by nuclear magnetic resonance
K. R. Wong and A. S. Verkman
To examine whether water transport in human platelets is mediated by an
aqueous pore or channel, the ratio of osmotic to diffusional water
permeability coefficients (Pf/Pd) was measured. Pd was measured from
protein spin-lattice relaxation times in a dense platelet suspension
(approximately 20% intracellular exchangeable water) using 20 mM solution
Mn as a paramagnetic quencher. The decay of magnetization was biexponential
with time constants of 1.3 and 6.9 ms (10 MHz, 37 degrees C), corresponding
to a Pd of (2.9 +/- 0.2) X 10(-3) cm/s (SE; n = 8). Pd did not depend on
concentrations of Mn (6-20 mM) or of platelets (2-4 X 10(10) platelets/ml),
but increased to 4.5 X 10(-3) cm/s with addition of gramicidin (6
micrograms/10(10) platelets). 54Mn uptake studies showed less than 1% of
equilibrium uptake of Mn into platelets in 30 min at 37 degrees C. The
activation energies (Ea) for Pd were 4.5 kcal/mol (less than 28 degrees C)
and 16.3 kcal/mol (greater than 28 degrees C). Pf was measured by a
stopped-flow light scattering technique as reported previously [M. M. Meyer
and A. S. Verkman, Human platelet osmotic water and nonelectrolyte
transport, Am. J. Physiol. 251 (Cell Physiol. 20): C549-C557, 1986], in
which the time course of platelet volume was measured in response to a 100
mM inwardly directed sucrose gradient. At 37 degrees C, Pf was (2.7 +/-
0.2) X 10(-3) cm/s and independent of [Mn]. The measured platelet Pf/Pd of
0.93 +/- 0.1 suggests that unlike water transport in erythrocytes, platelet
water transport is not associated with an aqueous channel.
