Rb. Bajnath et al., CHARACTERIZATION OF SWELLING-INDUCED ION-TRANSPORT IN HT-29CL.19A CELLS - ROLE OF INORGANIC AND ORGANIC OSMOLYTES DURING REGULATORY VOLUME DECREASE, Pflugers Archiv, 433(3), 1997, pp. 276-286
Combined intracellular and transepithelial potential and resistance me
asurements were performed to localize the ion conductances activated b
y hypo-osmotic shock of cultured human colonic carcinoma cells (HT-29C
l.19A). Furthermore, the effect of cell swelling induced by a hypo-osm
otic solution on the intracellular Ca2+ activity [Ca2+](i) and release
of amino acids into the extracellular solution was examined, Applicat
ion of a 40% hypo-osmotic solution on both sides of confluent monolaye
rs induced a hyperpolarization of the intracellular potential caused b
y increased K+ conductance of the basolateral membrane, followed by a
sustained depolarization due to increased Cl- conductance in the apica
l and basolateral membranes. Usually no transepithelial current occurr
ed, presumably because of random distribution of Cl- channels. However
, in some monolayers cell swelling induced a transepithelial Cl- curre
nt because of a more pronounced expression of volume-sensitive Cl- cha
nnels in the apical membrane. Exposure to hypo-osmotic solution increa
sed [Ca2+](i) transiently. The increase of [Ca2+](i) was also observed
to occur in the presence of the muscarinic receptor agonist carbachol
or the inhibitor of the microsomal Ca2+-ATPase thapsigargin (TG), whi
ch prevented carbachol-induced Ca2+ release, suggesting that cell swel
ling recruits Ca2+ from a different source compared to carbachol or TG
. Following incubations with hypo-osmotic solutions, about 60% of the
intracellular free amino acids including aspartate, glutamate, glycine
and taurine was released. It is concluded that the regulatory volume
decrease (RVD) in HT-29Cl.19A colonocytes is achieved by activation of
K+ and Cl- conductances, resulting in net loss of salt, as well by ex
trusion of amino acids.