(1) Desert gopher tortoises also store dilute urine that buffers evaporative loss and allows them to hold blood osmotic concentration constant, at least until bladder contents become isosmotic with blood.(2) Replacement of NaCl for isosmotic sorbitol produced a slight depolarization of the membrane.(3) Control experiments confirmed that no volume change occurred following perfusion of cells with isosmotic media.(4) A control experiment was performed for each group, in which cells were perfused with isosmotic media.(5) This led us to the hypothesis that terrestrial crabs have the option of directing isosmotic urine to organs that, unlike the antennal gland, are capable of producing strong gradients.
