Mechanisms of cell volume regulation in the proximal segment of the Malpighian tubule of Rhodnius neglectus

The cell volume regulation of the lower segment cells of the Malpighian tubule of Rhodnius neglectus in anisosmotic media was evaluated by using video-optic techniques. When the medium osmolality was increased with addition of 100 mM mannitol the cells shrank to a minimum of 16.84 +/- 2.62% and subs...

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Bibliographic Details
Published in:The Journal of membrane biology 1995-07, Vol.146 (1), p.47-57
Main Authors: Arenstein, I.R. (Universidade de Sao Paulo (Brazil)), Caruso-Neves, C, Onuchic, L.F, Lopes, A.G
Format: Article
Language:English
Subjects:
Animals
ANION
ANIONES
ANIONS
CATION
CATIONES
CATIONS
Cell Size - drug effects
Cell Size - physiology
CELLS
CELLULE
CELULAS
Ethacrynic Acid - pharmacology
Furosemide - pharmacology
ION
ION TRANSPORT
ION UPTAKE
IONES
IONS
Male
Malpighian Tubules - physiology
Mannitol - pharmacology
Microscopy, Video
Osmolar Concentration
OSMOLARITY
OSMOREGULACION
OSMOREGULATION
OSMOTIC PRESSURE
PRESION OSMOTICA
PRESSION OSMOTIQUE
REGULATORY VOLUME DECREASE
REGULATORY VOLUME INCREASE
RHODNIUS
Rhodnius - physiology
SISTEMA UROGENITAL
SYSTEME UROGENITAL
UROGENITAL SYSTEM
VOLUME
VOLUMEN
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Summary:The cell volume regulation of the lower segment cells of the Malpighian tubule of Rhodnius neglectus in anisosmotic media was evaluated by using video-optic techniques. When the medium osmolality was increased with addition of 100 mM mannitol the cells shrank to a minimum of 16.84 +/- 2.62% and subsequently swelled towards their initial volume undergoing a typical regulatory volume increase (RVI). Replacement of either K+ or Cl- or HCO(3-) by Na+, gluconate and phosphate, respectively, abolished the RVI response. Furthermore, the substitution of Na+ by tetramethylammonium (TMA+) in isosmotic conditions led to cellular swelling and death. Addition of either amiloride 10(-4) M, anthracene-9-COOH 5 x 10(-4) M, furosemide 5 x 10(-4) M or ethacrynic acid 5 x 10(-5) M, also abolished RVI. On the other hand, addition of either Ba2+ 10(-3) M, SITS 5 x 10(-4) M, ouabain 10(-3) M or vanadate 10(-3) M, did not change the RVI response. When the tubules were incubated in hyperosmotic media with EGTA 2 mM or verapamil 10(-6) M, the RVI response was abolished. In contrast, a decrease of NaCl concentration from 129 to 79 mM induced a cell swelling to a maximum of 33.11 +/- 1.73%, but the cells maintained swollen, only partially regulating their volume. These results show that the proximal cells of Malpighian tubule of R. neglectus are able to regulate their volume in hyperosmotic but only partially regulating in hyposmotic solutions. The mechanisms in RVI involve Na+, K+, Cl-, Ca2+ and HCO(3-) transport pathways and a ouabain-insensitive ATPase stimulated by Na+.
ISSN:0022-2631
1432-1424
DOI:10.1007/BF00232679