3-O-methylglucose as probe of cytoplasmic volumes

The intracellular volume of distribution (V) of 3-O-methylglucose (3OM), as calculated from mean artery-to-vein transit times (t)in the rabbit kidney, has been proposed as measure of cytoplasmic volume in renal cortex. This hypothesis requires that the non-concentrative uptake of the sugar be flow-dependent rather than diffusion-limited, and that total cell H2O (VHOH) exceed V3OM by a volume presumably reflecting that of 3OM-impermeable organelles. Diffusion-dependence of the calculated V3OM could be excluded by the finding that lengthening of t does not alter 3OM uptake. Determination of VHOH in kidney is complicated by presence of the luminal fluid compartment. VHOH and V3OM were therefore compared in leucocytes freshly prepared from rat blood; V3OM was found to equal 40% of VHOH. There is no evidence to suggest concentrative 3OM uptake by these cells; 3OM-impermeable organelles therefore occupy 60% of VHOH. These findings support the equation of V3OM with the cytoplasmic volume. As volume control is a basic function of intact cells, convenient determination of VHOH and V3OM on small numbers of readily available nucleated cells may prove useful in detecting early cytotoxic effects in vivo or in vitro.