title: The proximal straight tubule (PST) basolateral cell membrane water channel: selectivity characteristics.
abstract: Proximal straight tubules (PST) were dissected from rabbit kidneys, held by crimping pipettes in a chamber and bathed in a buffered isosmotic (295 mOsm/kg) solution containing 200 mM mannitol (MBS). Changes in tubule diameter were monitored on line with an inverted microscope, TV camera and image processor. The PST were then challenged for 20 sec with MBS made 35 mOsm/kg hyperosmotic by addition of either NaCl, KCl, mannitol (M), glycerol (G), ethylene glycol (E), glycine (g), urea (U), acetamide (A) or formamide (F). With NaCl, KCl, M, G, E, g, U, and A, tubules shrunk osmometrically within 0.5 sec and remained shrunk for as long as 20 sec without recovering their original volume (sometimes A showed some recovery). PST barely shrunk with F and quickly recovered their original volume. The permeability coefficients were 0 microns/sec (NaCl, M, g, E and U), 1 micron/sec (A), 84 microns/sec (F) and 0.02 micron/sec (G). The reflection coefficients sigma = 1.0 (NaCl, KCl, M, G, E, g and U), 0.95 (A) and 0.62 (F). Similar sigma values were obtained by substituting 200 mOsm/kg M in MBS by either NaCl, KCl, G, E, g, U, a or F. The olive oil/water partition coefficients are 5 (M), 15 (U), 85 (A) and 75 (F) (all x 10(-5)). Thus, part of F permeates the cell membrane through the lipid bilayer. The probing molecules van der Waals diameters are 7.4 x 8.2 x 12.0 (M), 3.6 x 5.2 x 5.4 (U), 3.8 x 5.2 x 5.4 (A) and (3.4 x 4.5 x 5.4 (F) A.(ABSTRACT TRUNCATED AT 250 WORDS)
authors.affiliation: Instituto Venezolano de Investigaciones Científicas, IVIC, Caracas, Venezuela.
authors.forename: A M
authors.initials: AM
authors.lastname: Gutiérrez
authors.forename: E
authors.initials: E
authors.lastname: González
authors.forename: M
authors.initials: M
authors.lastname: Echevarría
authors.forename: C S
authors.initials: CS
authors.lastname: Hernández
authors.forename: G
authors.initials: G
authors.lastname: Whittembury
mesh_terms: D000818:Animals; D051399:Aquaporin 2; D051403:Aquaporin 6; D020346:Aquaporins; D001485:Basement Membrane / Q000378:metabolism*; D001692:Biological Transport / Q000187:drug effects; D002462:Cell Membrane / Q000378:metabolism; D002463:Cell Membrane Permeability / Q000187:drug effects; D007473:Ion Channels; D007687:Kidney Tubules, Proximal / Q000166:cytology / Q000378:metabolism*; D008353:Mannitol / Q000494:pharmacology; D009994:Osmolar Concentration; D011817:Rabbits; D014867:Water / Q000378:metabolism*
chemical_list: D051399:Aquaporin 2; D051403:Aquaporin 6; D020346:Aquaporins; D007473:Ion Channels; D014867:Water; D008353:Mannitol