Cytoskeletal disruption in A6 kidney cells: impact on endo/exocytosis and NaCl transport regulation by antidiuretic hormone.
Antidiuretic hormone (ADH; 2.5 x 10(-8) M vasotocin) produces a stimulation of apical fluid phase endocytosis, protein secretion and NaCl reabsorption in Xenopus laevis A6 distal nephron cell epithelia pretreated with aldosterone (10(-6) M). The increase of NaCl transport is mediated by a sequential opening of apical Cl and Na conductances. The aim of this study was to characterize the actin and tubulin cytoskeleton of A6 cells and to assess the impact of its disruption on baseline and ADH-induced apical vesicular membrane movements and ion transport to test for possible functional links. The microfilament (MF) and microtubule (MT) networks and their disruption were visualized by confocal laser microscopy. Conditions of depolimerization were selected, by cytochalasin D or cold and nocodazole, respectively. MF disruption produced an increase in baseline apical protein secretion (exocytic movements) (plus 18%) and a decrease of its induction by ADH (minus 35%). MF disruption also increased baseline horseradish peroxidase uptake (endocytic movements) (plus 21%), however, without affecting its ADH-induced increase. In the case of MT disruption, the ADH-induced stimulation of both protein secretion and fluid phase endocytosis was decreased by 70 and 44%, respectively. At the ion transport level, MF and MT disruption only insignificantly affected the ADH-induced Cl conductance, while they decreased the ADH-induced stimulation of Na transport (amiloride-sensitive short-circuit current and conductance) by a factor of 2 to 4. In conclusion, both MT and MF disruption decrease ADH-induced apical protein secretion and Na conductance, while the ADH-induced apical Cl conductance is not significantly affected. Taken together the data support the hypothesis that the modulation of Na channel expression by apical vesicular membrane movements plays a role in Na transport expression and its regulation by ADH.
Verrey
F
F
Institute of Physiology, University of Zürich, Switzerland.
Groscurth
P
P
Bolliger
U
U
D008841:Actin Cytoskeleton / Q000187:drug effects / Q000502:physiology / Q000648:ultrastructure; D000199:Actins / Q000032:analysis*; D000450:Aldosterone / Q000494:pharmacology; D000818:Animals; D001692:Biological Transport / Q000187:drug effects; D001704:Biopolymers; D002460:Cell Line; D016764:Cell Polarity; D018118:Chloride Channels / Q000187:drug effects / Q000378:metabolism; D003080:Cold Temperature; D000242:Cyclic AMP / Q000502:physiology; D015638:Cytochalasin D / Q000494:pharmacology; D003599:Cytoskeleton / Q000187:drug effects / Q000502:physiology*; D004705:Endocytosis / Q000187:drug effects*; D053503:Epithelial Sodium Channels; D004848:Epithelium / Q000187:drug effects / Q000502:physiology / Q000648:ultrastructure; D005089:Exocytosis / Q000187:drug effects*; D007686:Kidney Tubules, Distal / Q000187:drug effects* / Q000502:physiology / Q000648:ultrastructure; D008564:Membrane Potentials / Q000187:drug effects; D008855:Microscopy, Electron, Scanning; D008870:Microtubules / Q000187:drug effects / Q000502:physiology / Q000648:ultrastructure; D015739:Nocodazole / Q000494:pharmacology; D011506:Proteins / Q000378:metabolism; D015222:Sodium Channels / Q000187:drug effects / Q000502:physiology*; D012965:Sodium Chloride / Q000378:metabolism*; D000254:Sodium-Potassium-Exchanging ATPase / Q000378:metabolism; D014404:Tubulin / Q000032:analysis*; D014667:Vasopressins / Q000494:pharmacology*; D014982:Xenopus laevis
D000199:Actins; D001704:Biopolymers; D018118:Chloride Channels; D053503:Epithelial Sodium Channels; D011506:Proteins; D015222:Sodium Channels; D014404:Tubulin; D014667:Vasopressins; D015638:Cytochalasin D; D012965:Sodium Chloride; D000450:Aldosterone; D000242:Cyclic AMP; D000254:Sodium-Potassium-Exchanging ATPase; D015739:Nocodazole