Control of Glycogenolysis in the Toad's Urinary Bladder: THE EFFECT OF ANAEROBIOSIS, SODIUM TRANSPORT, AND ARGININE VASOTOCIN

Abstract

Abstract The control of glycogenolysis in the urinary bladder of the toad (Bufo marinus) in vitro has been examined by measuring the concentration of glycogenolytic intermediates and cofactors in the tissue. When the rate of glycogenolysis was increased by anaerobiosis, metabolite levels indicated activation of phosphofructokinase and pyruvate kinase. The activation of phosphofructokinase was probably secondary to a fall in the concentration of adenosine triphosphate and a rise in the concentration of adenosine mono- and diphosphate and inorganic phosphate. Activation of pyruvate kinase may have been secondary to a fall in the concentration of adenosine triphosphate and a rise in adenosine diphosphate or the rise in the concentration of fructose 1,6-diphosphate or both. Incubation with arginine vasotocin in a Ringer's solution containing sodium stimulated glycogenolysis under aerobic or anaerobic conditions. The hormone caused activation of phosphorylase, phosphofructokinase, and pyruvate kinase without marked changes in the concentration of cofactors. Since arginine vasotocin affects the toad bladder by stimulating adenyl cyclase activity, it is speculated that adenosine 3',5'-monophosphate activates phosphorylase, resulting in a rise in the concentration of fructose 6-phosphate, which in turn activates phosphofructokinase, resulting in a rise in the concentration of fructose, 1,6-diphosphate, which may activate pyruvate kinase. When sodium transport was inhibited by incubating the bladder with ouabain or in a Ringer's solution in which tris(hydroxymethyl)aminomethane ions replaced all of the sodium ions, the rate of glycogenolysis fell as a result of inhibition at phosphofructokinase. There were no significant changes in the concentration of adenosine mono-, di-, or triphosphate or inorganic phosphate. In contrast to experiments in a Na+ Ringer's solution, arginine vasotocin did not stimulate glycogenolysis in bladders incubated in a Tris+ Ringer's solution. Metabolite levels indicated only slight activation of phosphorylase and no activation of phosphofructokinase or pyruvate kinase. Again, no change in the concentration of cofactors was detected. It is concluded that phosphorylase, phosphofructokinase, and pyruvate kinase are glycogenolytic control points in the toad bladder responding to changes in the concentration of cofactors In addition, it is apparent that the rate of sodium transport affects the activity of these enzymes through an unknown pathway.