Dynamics of Ca 2+ i and pH i in Ehrlich ascites tumor cells after Ca 2+ -mobilizing agonists or exposure to hypertonic solution

Abstract

Intracellular free calcium concentration ([Ca2+]i) and intracellular pH (pHi) were monitored in Ehrlich ascites tumor cells using Fura-2 or 2',7',-bis-(2-carboxyethyl)-5,6-carboxyfluorescein (BCECF), or both probes in combination. An increase in [Ca2+]i induced by thrombin or bradykinin, agonists known to elicit transient cell shrinkage in these cells, evoked a transient intracellular acidification, followed by an alkalinization. The latter was due to activation of a Na+/H+ exchanger and was inhibited under conditions preventing agonist-induced cell shrinkage without preventing the increase in [Ca2+]i. In contrast, a smaller, slower increase in [Ca2+]i elicited by thapsigargin did not cause cell shrinkage, and did not activate the Na+/H+ exchanger. Exposure to hypertonic solution was not associated with an increase in [Ca2+]i, but elicited an intracellular alkalinization similar to that induced by thrombin or bradykinin, via activation of the Na+/H+ exchanger. Thus, activation of the exchanger by the Ca2+-mobilizing agonists is suggested to be secondary to the cell shrinkage induced by these compounds. NH4Cl-induced intracellular alkalinization resulted in an increase in [Ca2+]i, apparently via stimulation of Ca2+ influx, whereas shrinkage-induced intracellular alkalinization did not stimulate Ca2+ influx. Thus, cell shrinkage appears to inhibit the Ca2+ influx otherwise resulting from alkalosis. In agreement with that notion, thapsigargin-induced Ca2+ influx was inhibited by cell shrinkage.

Effects of Ammonia Exposition on Glioma Cells: Changes in Cell Volume and Organic Osmolytes Studied by Diffusion-Weighted and High-Resolution NMR Spectroscopy

“…In addition to Gln, myo-Ins and taurine, the intracellular concentrations of several other metabolites depend on the cell volume. Consistent with the cell swelling, we observed already 3 h after ammonia treatment a reduction in the glycine concentration, an amino acid contributing also to cellular osmolarity [36]. The signal intensity of choline-containing metabolites, which also have been found to be lowered in 1 H MRS brain spectra of patients with chronic HE [13,15,16,37], decreases considerably.…”

“…Portacaval anastomosis increases astrocytic pH i in rat brains, which may be a necessary concomitant of cellular volume regulatory processes [34]. Thus, it is conceivable that by analogy to acidosis-induced cell swelling [35], the alkalosis evoked by NH 4 Cl [36] causes a transient cell shrinking.…”

Interdependence of Ca2+ and proton movements in trout hepatocytes

“…In parallel to the increase in [Ca 2+ ] i , ionomycin and thapsigargin induced a biphasic response in pHi, a brief acidification followed by a sustained alkalinization. Similar observations have been reported for other cell lines in response to agents known to raise [Ca 2+ ] i , such as ionomycin Slotki et al, 1989;Slotki et al, 1993) or the hormones bradykinin (Slotki et al, 1993;Pedersen et al, 1998), thrombin (Zavoico et al, 1986;Pedersen et al, 1998), angiotensin II and arginine vasopressin (Ganz et al, 1988).…”

Metabolic and ionic responses of trout hepatocytes to anisosmotic exposure

“…Changes of [Ca 2+ ]i under hyperosmotic conditions have received comparatively little attention, but an increase (frog skeletal muscle; Chawla et al, 2001), no change (Ehrlich ascites tumour cells; Pedersen et al, 1998) and even a decrease of [Ca 2+ ]i have been reported (rabbit proximal tubular cells; Raat et al, 1995). In trout hepatocytes, hyperosmolarity unequivocally caused an increase of [Ca 2+ ]i that was apparent both at the population and the single cell level (Figs·5,·6).…”