Enzymatic modulation of cell volume in C6 glioma cells.
We monitored the volume of C6 glioma cells in suspension using a Coulter Counter and exposed the cells to micromolar or nanomolar levels of collagenase or clostripain. In 13 experiments, type IV collagenase (310 units ml-1; approximately 3 microM L-1) decreased the volume by 8-12%, 8 min after addition. In 13 of 21 experiments, the volume decrease was followed by a volume regulatory increase (VRI) back to control levels in the continued presence of collagenase. The shrinkage evoked by type IV collagenase was eliminated by heat-inactivation of the enzyme preparation. A highly purified collagenase (type VII) at the same concentration evoked a relatively minor decrease in volume. A well-known contaminating protease present in type IV collagenase, clostripain, which specifically cleaves arginyl peptide bonds, evoked a 7 +/- 2% shrinkage (100 nM L-1, 7 experiments). Clostripain did not evoke a volume regulatory increase. The initial velocity of shrinkage evoked by clostripain (0.0012 pL min-1, 0.0034 pL min-1, 0.0132 pL min-1; 1 pL = 10(-12) liters) scaled with its concentration (1 nM L-1, 10 nM L-1, 100 nM L-1). The effect of clostripain was inhibited by heat-inactivation of the enzyme. Leupeptin, an inhibitor of clostripain, prevented the decrease in volume evoked by clostripain. The activity of stretch-activated ion channels was unaffected by type IV collagenase. Barium, cesium, amiloride, DIDS, or bumetanide failed to block the shrinkage evoked by type IV collagenase. These results demonstrate that clostripain, present in crude collagenase enzyme preparations, causes the shrinkage, and that C6 glioma cells can undergo a volume regulatory increase at virtually constant osmotic pressure. In addition, cleavage of a cell surface moiety, which contains arginine, and possibly proline, causes shrinkage. This moiety may be part of the extracellular or intracellular matrix providing mechanical support to the cells. VRI reflect actions of another substance in the type IV crude collagenase preparations, on a receptor independent of the arg-pro moiety. The enzymatic modulation of glioma cell volume by these two receptors may reflect a new mechanism by which such cells, and possibly other glia, regulate their contact area and interactions with other cells in the central nervous system.[1]References
- Enzymatic modulation of cell volume in C6 glioma cells. Bowman, C.L., Yohe, L., Lohr, J.W. Glia (1999) [Pubmed]
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