AJP - Regulatory, Integrative and Comparative Physiology, Vol 258, Issue 4 1022-R1033, Copyright © 1990 by American Physiological Society
Possible role of basolateral cell membrane in proximal renal tubule osmoregulation
D. Terreros, H. Kanli and J. Coombs
Laboratory Service, Veterans Administration Medical Center, Salt Lake City, Utah 84148.
The cellular response to hypotonic stimulation was studied with videometric
methods in 266 proximal renal tubules dissected from Carassius auratus
(goldfish). In hypotonic solutions (low NaCl), cells underwent rapid
swelling followed by gradual shrinking toward isotonic volume
(volume-regulatory decrease phase, VRD). Hypothermia (8 degrees C),
increased extracellular potassium (15, 25, and 40 mM), quinine (0.1 mM),
barium (0.5 mM), 4,4'-diisothio-cyanostilbene-2,2'-disulfonic acid (DIDS;
0.02 mM), acetazolamide (0.1 mM), decrements in extracellular bicarbonate,
and increases in extracellular chloride impaired VRD. Ouabain (1.0 mM),
furosemide (0.1 mM), and the chloride channel blocker
5-nitro-2-(3-phenylpropylalanine) benzoate (NPPB; 0.001 mM) had no effect.
While VRD occurred in the absence of extracellular calcium influx, addition
of the calcium ionophore A23187 (0.01 mM) in the presence of ethylene
glycol-bis(beta-aminoethyl ether)-N,N,N',N'-tetraacetic acid (EGTA; 2.0 mM)
impaired this process both in acidic and alkaline media. Trifluoroperazine
(0.01 mM) reversibly inhibited VRD. The effect of this calmodulin inhibitor
could not be overridden with the cationic ionophore gramicidin (0.5
microM). The data suggest that Carassius proximal renal tubular cells
volume regulate in hypotonic solutions by the loss of KCl and osmotically
obligated water. We postulate that the main efflux of potassium is through
a calcium-gated potassium channel with its counter ion extruded through a
calmodulin-regulated Cl(-)-HCO3- exchanger.
