Ir. Arenstein et al., MECHANISMS OF CELL-VOLUME REGULATION IN THE PROXIMAL SEGMENT OF THE MALPIGHIAN TUBULE OF RHODNIUS-NEGLECTUS, The Journal of membrane biology, 146(1), 1995, pp. 47-57
The cell volume regulation of the lower segment cells of the Malpighia
n tubule of Rhodnius neglectus in anisosmotic media was evaluated by u
sing video-optic techniques. When the medium osmolality was increased
with addition of 100 mM mannitol the cells shrank to a minimum of 16.8
4 +/- 2.62% and subsequently swelled towards their initial volume unde
rgoing a typical regulatory volume increase (RVI). Replacement of eith
er K+ or Cl- or HCO3- by Na+, gluconate and phosphate, respectively, a
bolished the RVI response. Furthermore, the substitution of Na+ by tet
ramethylammonium (TMA(+)) in isosmotic conditions led to cellular swel
ling and death. Addition of either amiloride 10(-4) M, anthracene-9-CO
OH 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 n
ot change the RVI response. When the tubules were incubated in hyperos
motic 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. The
se results show that the proximal cells of Malpighian tubule of ii. ne
glectus are able to regulate their volume in hyperosmotic but only par
tially regulating in hyposmotic solutions. The mechanisms in RVI invol
ve Na+, K+, Cl-, Ca2(+) and HCO3- transport pathways and a ouabain-ins
ensitive ATPase stimulated by Na+.