Energy‐dependent volume regulation in primary cultured cerebral astrocytes

Abstract

Cell volume regulation and energy metabolism were studied in primary cultured cerebral astrocytes during exposure to media of altered osmolarity. Cells suspended in medium containing 1/2 the normal concentration of NaCl (hypoosmotic) swell immediately to a volume 40-50% larger than cells suspended in isoosmotic medium. The cell volume in hypoosmotic medium then decreases over 30 min to a volume approximately 25% larger than cells in isoosmotic medium. In hyperosmotic medium (containing twice the normal concentration of NaCl), astrocytes shrink by 29%. Little volume change occurs following this initial shrinkage. Cells resuspended in isoosmotic medium after a 30 min incubation in hypoosmotic medium shrink immediately to a volume 10% less than the volume of cells incubated continuously in isoosmotic medium. Thus, the regulatory volume decrease (RVD) in hypoosmotic medium involves a net reduction of intracellular osmoles. The RVD is partially blocked by inhibitors of mitochondrial electron transport but is unaffected by an inhibitor of glycolysis or by an uncoupler of oxidative phosphorylation. Inhibition of RVD by these metabolic agents is correlated with decreased cellular ATP levels. Ouabain, added immediately after hypoosmotic induced swelling, completely inhibits RVD, but does not alter cell volume if added after RVD has taken place. Ouabain also inhibits cell respiration 27% more in hypoosmotic medium than in isoosmotic medium indicating that the (Na,K)-ATPase-coupled ion pump is more active in the hypoosmotic medium. These data suggest that the cell volume response of astrocytes in hypoosmotic medium involves the net movement of osmoles by a mechanism dependent on cellular energy and tightly coupled to the (Na,K)-ATPase ion pump. This process may be important in the energy-dependent osmoregulation in the brain, a critical role attributed to the astrocyte in vivo.

Contribution of chloride channels to volume regulation of cortical astrocytes

“…In the presence of continued hypotonicity, cells began to decrease their volume as previously demonstrated by others (14,25). Measurements were taken for 45 min, and Fig.…”

“…These data suggest that Cl Ϫ flux through ion channels rather than transporters is essential for volume regulation of cultured astrocytes in response to hypotonic challenge. glia; ion channels; Coulter counter MOST CELLS POSSESS MECHANISMS to control or regulate their volume (18), and volume regulation has been clearly demonstrated for cultured rat cortical astrocytes in response to hypotonic challenge (14,25). However, it appears that the mechanisms of volume regulation are ineffective in astrocytes in the brain after neurological insult, as swelling of astrocytes is a major complicating factor of conditions including ischemia, trauma, hyponatremia, and hepatic encephalopathy (16).…”

Channels and Volume Changes in the Life and Death of the Cell

“…At the same time, cells set in motion an active regulatory process directed to partially or fully restore the original volume (Cala, 1977;Olson et al, 1986;Hoffmann, 1992;Okada, 2004). This adaptive mechanism, which has been highly preserved during evolution, essentially consists of the redistribution of osmotically active solutes in the necessary direction to equilibrate water fluxes facing the new osmotic condition (Lang, 2007;see Hoffmann et al, 2009 for a comprehensive review of cell volume regulation).…”

Swelling-induced release of glutamate, aspartate, and taurine from astrocyte cultures

“…Astrocytes in vitro have been shown to exhibit RVD after swelling in hypotonic media (Kempski et al, 1983;Kimelberg and Frangakis, 1985;Olson et al, 1986) which is associated with an increased permeability to mannitol (Kimelberg and Goderie, 1988) reversible membrane depolarization (Kimelberg and O'Connor, 1988) and release of 3H-taurine (Pasantes-Morales and Schousboe, 1988).…”