Fig. 1. Representative ³¹P-NMR spectra arranged in time series during an extreme hypo-osmotic treatment. From left to right, the peaks are sugar phosphate, inorganic phosphate (P_i), arginine phosphate (tallest peak) and the , and ß peaks of ATP. The tissue was acclimated to 35 salinity and exposed to a medium simulating a transfer to 5. Each spectrum was collected over a period of 10 min, so the total experimental time was 2 h. The first spectrum was collected under control conditions in which the tissue was superfused with a medium of 960 mosmol l^-1, and all subsequent spectra were collected while the muscle was superfused with a medium of 640 mosmol l^-1. Several such stability experiments were conducted for the hypo- and hyperosmotic treatments and, in each case, the arginine phosphate, ATP and P_i peak areas remained constant. This indicates that the tissues were not energetically compromised during the flux experiments.