Cell content of phosphatidylinositol (4,5)bisphosphate in Ehrlich mouse ascites tumour cells in response to cell volume perturbations in anisotonic and in isosmotic media

• Published in: The Journal of physiology Vol. 582; no. 3; pp. 1027 - 1036
• Main Authors: Nielsen, Doris K., Jensen, Annelie Kolbjørn, Harbak, Henrik, Christensen, Søren C., Simonsen, Lars Ole
• Format: Journal Article
• Language: English
• Published: Oxford, UK The Physiological Society 01.08.2007; Blackwell Publishing Ltd; Blackwell Science Inc
• Subjects: Animals; Body Water - physiology; Carcinoma, Ehrlich Tumor - pathology; Carcinoma, Ehrlich Tumor - physiopathology; Cell Size; Culture Media; Female; Inositol Phosphates - physiology; Kinetics; Mice; Mice, Inbred Strains; Phosphatidylinositol 4,5-Diphosphate - metabolism; Related Papers
• ISSN: 0022-3751; 1469-7793
• DOI: 10.1113/jphysiol.2007.132308

The labelling pattern of cellular phosphoinositides (PtdIns P n ) was studied in Ehrlich ascites cells labelled in vivo for 24 h with myo -[2- 3 H]- or l - myo -[1- 3 H]inositol and exposed to anisotonic or isosmotic volume perturbations. In parallel experiments the cell volume ([ 14 C]3-OMG space) was monitored. In hypotonic media the cells initially swelled osmotically and subsequently as expected showed a regulatory volume decrease (RVD) response. Concurrently, the cell content of PtdIns P 2 showed a marked, transient decrease and the content of PtdIns P a small, transient increase. The changes in PtdIns P 2 and PtdIns P content increased progressively with the extent of hypotonicity (in the range 1.00–0.50 relative osmolarity). No evidence was found for either hydrolysis of PtdIns P 2 or formation of PtdIns P 3 . In hypertonic medium (relative osmolarity 1.50), cells initially shrank osmotically and subsequently as expected showed a small regulatory volume increase (RVI) response. Concurrently, the cell content of PtdIns P 2 showed a marked increase and the content of PtdIns P a small decrease, i.e. changes in the opposite direction of those seen in hypotonic media. In isosmotic media with high (100 m m ) or low (0.8 m m ) K + concentration, cells slowly swelled or shrank due to uptake or loss of isosmotic KCl. Under these conditions, with largely unchanged intracellular ionic strength, the cell content of PtdIns P 2 and PtdIns P remained constant. Our results show that PtdIns P 2 is not volume sensitive per se , and moreover that the regulatory volume adjustments in Ehrlich ascites cells are not mediated by PtdIns P 2 hydrolysis and its subsequent production of second messengers. The simplest interpretation of the observed effects would be that PtdIns P 2 is controlled by ionic strength, probably via activation/inhibition of phosphoinositide-specific phosphatases/kinases. In Ehrlich ascites cells, as shown previously, the opposing ion channels and transporters activated during RVD and RVI, respectively, are controlled with tight negative coordination by a common cell volume ‘set-point’ that is shifted in anisotonic media, but unchanged during cell swelling in isosmotic high K + medium. We hypothesize that PtdIns P 2 might orchestrate this ‘set-point’ shift.