AJP - Cell Physiology, Vol 263, Issue 4 C901-C907, Copyright © 1992 by American Physiological Society
Organic osmolytes increase cytoplasmic viscosity in kidney cells
N. Periasamy, H. P. Kao, K. Fushimi and A. S. Verkman
Department of Medicine, University of California, San Francisco 94143-0532.
The hypothesis was tested that accumulation of osmolytes by kidney cells
grown in hyperosmolar media decreases the rotational and translational
mobilities of small polar solutes in the cytosolic compartment. Rotational
mobility was measured by the picosecond rotational correlation times (tau
c) of 2',7'-bis(2-carboxyethyl)-5(6)carboxylfluorescein (BCECF) by
multiharmonic microfluorimetry. In isolated segments of rabbit proximal
tubule, thick ascending limb, and cortical collecting duct that were
perfused and bathed in 300 mosM media, tau c were in the range 180-250 ps,
corresponding to apparent rotational viscosities (eta r) of 1.1-1.5 cP. In
cortical collecting tubule, eta r was not influenced by serosal
vasopressin. In Madin-Darby canine kidney (MDCK) cells grown in 300-1,200
mosM media, eta r increased progressively by up to a factor of 1.38 +/-
0.03; measurements of tau c and macroscopic viscosity in artificial
solutions containing osmolytes supported the hypothesis that the increased
eta r was due to accumulation of organic osmolytes. BCECF translational
mobility was measured by fluorescence photobleaching recovery using a
focused 1.2-microns diameter Ar laser beam at 488 nm. Recovery half-times
were 36 +/- 3 (SE) ms (n = 10) in MDCK cells grown in 300 mosM media and 62
+/- 3 ms (n = 10) when grown in 1,200 mosM media. The results suggest that
accumulation of osmolytes by renal cells is associated with significantly
increased cytosolic viscosity. The increased viscosity would slow enzymatic
and transport processes in the cytosolic compartment.
