Regulation of cell volume by glycosaminoglycans

Abstract

Cell volume is regulated by a delicate balance between ion distribution across the plasma membrane and the osmotic properties of intra- and extracellular components. Using a fluorescent calcein indicator, we analysed the effects of glycosaminoglycans on the cell volume of hyaluronan producing fibroblasts and hyaluronan deficient HEK cells over a time period of 30 h. Exogenous glycosaminoglycans induced cell blebbing after 2 min and swelling of fibroblasts to about 110% of untreated cell volume at low concentrations which decreased at higher concentrations. HEK cells did not show cell blebbing and responded by shrinking to 65% of untreated cell volume. Heparin induced swelling of both fibroblasts and HEK cells. Hyaluronidase treatment or inhibition of hyaluronan export led to cell shrinkage indicating that the hyaluronan coat maintained fibroblasts in a swollen state. These observations were explained by the combined action of the Donnan effect and molecular crowding.

Regulation of intracellular pH by glycosaminoglycans

“…Hyaluronidase digestion or inhibition of hyaluronan export led to intracellular alkalization indicating the phenomena were physiological. As discussed previously (Joerges et al, ), the concentration range of glycosaminoglycans up to 2 mg/ml were also physiological. Adjustment was extremely fast, because the final intracellular pH had been already reached after 5 sec, the earliest measurable time point.…”

“…Donnan effects of extracellular glycosaminoglycans were also responsible for membrane depolarization (Hagenfeld et al, 2010) which were attributed to K þ influx or to cell swelling and blebbing which were mediated by volume sensitive chloride influx (Joerges et al, 2012). Similarly, extracellular hyaluronan caused Ca 2þ influx through postsynaptic Ca 2þ channels (Kochlamazashvili et al, 2010).…”

“…The intracellular pH is regulated together with other cellular properties such as membrane potential and cell volume (Fraser et al, ). Recently we described that extracellular glycosaminoglycans reduce the membrane potential by influx of extracellular K + ions (Hagenfeld et al, ) and influence the cell volume by influx of extracellular Cl − ions (Joerges et al, ). On the other hand, hyaluronan is synthesized at the inner side of plasma membranes (Prehm, ) and exported by the ABC transporters MRP5 from fibroblasts (Schulz et al, ) and CFTR from epithelial cells (Schulz et al, ).…”

Adsorption of Glycosaminoglycans to the Cell Surface Is Responsible for Cellular Donnan Effects

“…In conclusion, local glycosaminoglycans concentration led to Donnan effects that exceed their concentration in solution causing depolarisation of the membrane potential [Hagenfeld et al, ], cell swelling [Joerges et al, ] and intracellular acidification [Kathagen and Prehm, ].…”

“…Recently, we demonstrated that extracellular glycosaminoglycans have profound effects on fundamental cellular properties. They reduce the membrane potential [Hagenfeld et al, ], alter the cell volume [Joerges et al, ] and decrease the intracellular pH [Kathagen and Prehm, ]. These phenomena were independent of the CD44 receptor and can be explained by Donnan effects.…”