Isosmotic swelling of skate (Raja erinacea) red blood cells causes a volume regulatory release of intracellular taurine

Abstract

Animal cells swell when placed in a hypotonic medium and then regulate their volume by releasing intracellular solutes. The aim of this study was to determine whether hypoosmolarity or cell swelling is the stimulus that triggers the release of solutes. Swelling skate red blood cells (RBC) by placing them in isosmotic media containing rapidly penetrating solutes (NH4C1, ethylene glycol) caused increased release of taurine from the cells. Isosmotic swelling also increased the cellular levels of radiolabeled diacylglycerol, a second messenger previously implicated in volume regulation by skate RBC. These results indicate that the release of intracellular solutes by hypoosmotically stressed skate RBC is brought about by cell swelling.Animal cells generally swell when exposed to hypotonic media. The swelling is often followed by a regulatory volume decrease (RVD) that is due to the loss of intracellular solutes and accompanying water. Although a great deal is known about the physiological and biochemical mechanisms of RVD (see, for example, reviews by Grinstein et al., '84; Hoffman, '85; Eveloff and Warnock, ,871, little work has been done elucidating the physiological stimulus that triggers the response. It is not known whether the drop in medium osmolarity or the increase in cell volume and accompanying membrane stretching brings about the RVD in hypotonic medium. In the present study we used the skate RBC to differentiate between these two possibilities.We compared the release of intracellular taurine, a major organic osmolyte in skate red blood cells (RBC) (Boyd et al., '77; Leite and Goldstein, '871, following isosmotic expansion of RBC with the rapidly penetrating solutes NH4C1 and ethylene glycol with the response following hypoosmotic expansion. In addition we measured the levels of radiolabeled diacylglycerol (a second messenger implicated in the taurine response of hypoosmotically stressed skate RBC (McConnell and Goldstein, '88) in RBC expanded isosmotically. The results obtained indicate that cell volume expansion, not a drop in medium osmolarity, is the stimulus that triggers the RVD. MATERIALS AND METHODSAnimals and facilities Little skates (Raja erinacea) of both sexes and weighing 0.5-1.5 kg, were captured by dragnet off the coast of Mount Desert Island, Maine, or Cape Cod, Massachusetts. Fish were maintained in seawater tanks at 10-20°C for up to 10 days. Preparation of RBC suspensionFour to 10 ml of blood was drawn from a caudal vessel using a heparinized syringe fitted with a 2 1 gauge, 1" needle. Freshly drawn blood was placed into a chilled, thick-walled glass centrifuge tube and centrifuged for 5 minutes at top speed in an IEC Clinical Centrifuge fitted with an angle head. Plasma and buffy coat were removed, and RBC were washed once in 1 vol (relative to whole blood) of control elasmobranch incubation medium (EIM): 300 mM NaCl, 5.2 mM KCl, 2.7 mM MgS04, 5.0 mM CaC12, 15 mM Tris-HC1, 370 mM urea, pH = 7.5, osmolality = 940 m0sm). Supernatant and remaining buffy coat were removed again. ...

Effects of hyposmotic shock on taurine transport in isolated trout hepatocytes

“…This contribution has been described in invertebrates and also in mammalian tissues such as cardiac cells (Thurston, Hauhart & Naccarato, 1981), Ehrlich cells (Hoffmann & Lambert, 1983;Lambert, 1984;Lambert & Hoffmannn, 1993) (Fugelli & Thoroed, 1986;Kirk, Ellory & Young, 1992), the skate (Goldstein & Brill, 1990, the eel (Fincham, Wolowyk & Young, 1987) and the trout (Garcia-Romeu, Cossins & Motais, 1991), and also in the cyclostomes, hagfish and lamprey (Brill, Musch & Goldstein, 1992).…”

“…In fish, observations related to amino acids have been made with regard to cell volume regulation mostly on erythrocytes, in the flounder (Fugelli & Thoroed, 1986;Kirk, Ellory & Young, 1992), the skate (Goldstein & Brill, 1990, the eel (Fincham, Wolowyk & Young, 1987) and the trout (Garcia-Romeu, Cossins & Motais, 1991), and also in the cyclostomes, hagfish and lamprey (Brill, Musch & Goldstein, 1992).…”

The effect of a hyposmotic shock on amino acid efflux from lactating rat mammary tissue: stimulation of taurine and glycine efflux via a pathway distinct from anion exchange and volume‐activated anion channels

“…For example, a net loss of taurine, a non-protein amino acid, occurs during a RVD in fish red blood cells (e.g. see Fincham, Wolowyk & Young, 1987;Goldstein & Brill, 1990). Indeed, taurine and other amino acids, notably glycine and alanine, have been shown to contribute to a RVD in some mammalian cells, such as Ehrlich ascites tumour cells and rat heart (Thurston, Hauhart & Naccarato, 1981;Hoffmann & Lambert, 1983).…”

Osmolyte channel regulation by ionic strength in skate RBC

“…In many cells, the osmolyte channels show the properties of a swelling-activated anion channel (10,18,20). In fish erythrocytes, however, the osmolyte channel is proposed to be the anion exchanger band 3 or an associated channel (4,6,8,9,11,15).…”