STUDIES ON THE ISOLATED ISLET TISSUE OF FISH. II. THE EFFECT OF ELECTROLYTES AND OTHER FACTORS ON THE OXYGEN UPTAKE OF PANCREATIC ISLET SLICES OF TOADFISH, USING THE CARTESIAN DIVER MICRORESPIROMETER

Abstract

The metabolic activity of islet slices obtained from the toadfish, Opsanus tau, was measured in a Cartesian diver micro-respirometer under varying experimental conditions. The islet was cut into 8 slices each weighing approximately 0.1 to 0.2 mg wet weight. At the end of the experiment, the protein content of each slice was measured and the oxygen uptake was expressed as m[mu]l of O2/[mu]g protein/hour. The metabolic activity of islet slices was not affected by varying the pH of the medium between 6.2 and 8.0. Phosphate ion addition stimulated the oxygen uptake; maximal stimulation occurred when the phosphate concentration was 0.066[image]. The oxygen uptake was likewise increased when the tonicity of the suspending media was reduced; optimal respiration occurred in a hypotonic medium whose tonicity was equivalent to 0.075 [image] NaCl. This optimal tonicity is equivalent to a phosphate buffer concentration of 0.054 [image] and it is slightly sub-optimal with respect to phosphate ion concentration. High concentrations of Ca ion (0.001-0.002 [image]) inhibited the respiration of islet slices. Lower concentrations of Ca ion (0.0005 [image]), Mg ion (0.0002-0.01 [image]), serum protein addition, and small amounts of trace metals (boron, molybdenum, Fe, Mn, Zn) did not stimulate the respiration of islet tissue slices.