Regulatory volume decrease

In previous reviews on this matter by Gogelein [9] and myself [10] it has been pointed out that the Cl -channels of the central nervous system and of skeletal muscle are distinct from those of non-excitable cells. The latter entity is in itself obviously heterogeneous with respect to its occurrence and function. In apolar as well as in polarized cells Cl -channels may be involved in volume regulation. As a simple rule gating of K" - and Cl -channels is likely to occur whenever cell volume has to be down-regulated [11], as is the case in regulatory volume decrease of cell volume. A simple means to induce this phenomena is the exposure of cells to hypoosmolar solutions [12]. For example Cl -channels play an important role in... 

Doroshenko, P., Sabanov, V. and Doroshenko, N., 2001, Cell cycle-related changes in regulatory volume decrease and volume-sensitive chloride conductance in mouse fibroblasts. J Cell Physiol 187, 65-72. 

Shen, M. R., Yang, T. P. and Tang, M. J., 2002, A novel function of BCL-2 overexpression in regulatory volume decrease. Enhancing swelling-activated Ca2+ entry and CD channel activity. J Biol Chem 277, 15592-9. 

Valverde MA, Bond TD, Hardy SP, et al. The multidrug resistance P-glycoprotein modulates cell regulatory volume decrease. EMBO J 1996 15(17) 4460-4468. 

When cells are suddenly suspended in a hypoosmotic medium they initially swell as if they were perfect osmometers, but a few minutes later they down-regu-late their volume, thereby approaching the volume they had at the start. This behavior has been termed regulatory volume decrease (RVD). RVD, however, does not completely return the cell volume to normal (Figure 1). The extent of this remaining volume deviation, which is equivalent to a steady-state change in cell... 

Table 1. Ionic Mechanisms Involved in Regulatory Volume Decrease (RVD) and Increase (RVI)...

THE REGULATION OF CELL VOLUME REGULATORY VOLUME DECREASE (RVD)... 

Two ion channels are responsible for this regulatory volume decrease (RVD) a potassium channel and a chloride channel. Let us see how this regulatory volume decrease operates in lymphocytes. 

Figure 6a. Changes in lymphocyte volume during regulatory volume decrease (RVD). Lymphocytes were suspended in 0.6 isosmotic sodium chloride. Potassium and chloride channels were functional.

Figure 6c. Predicted changes in the permeability of the potassium and/or chloride channel during regulatory volume decrease.

After a cycle of cell swelling followed by regulatory volume decrease, we are left with lymphocytes having reduced intracellular concentrations of potassium and chloride. 

Figure 7a. Changes in cell volume during regulatory volume decrease (RVD) followed by regulatory volume increase (RVI) in lymphocytes. Only sodium/proton exchangers were functional (square). Both sodium/proton exchangers and chloride/bi-carbonate exchangers were functional (diamond).

Figure 7c, Changes in lymphocyte ions during regulatory volume decrease followed by regulatory volume increase.

Cell swelling leads to the activation of K+ and anion channels. Upon swelling, the K+ channel is probably activated by an increase of intracellular calcium activity. During swelling, electrolytes are released via these channels to achieve a regulatory volume decrease. 

Margalit A, Livne AA. Lipoxygenase product controls the regulatory volume decrease of human platelets. Platelets 1991 2 207-214. 

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