Regulation of glycolysis in the land snail Oreohelix during estivation and artificial hypercapnia
Abstract
Respiration rates, hemolymph acid-base variables, and metabolite levels were measured in the land snail Oreohelix during a brief period of estivation (4 days) and during exposure of non-estivating snails to elevated levels of ambient CO2 (34 and 58 mmHg). Respiration rate dropped during entry into estivation reflecting decreased glycolytic flux. Analyses of metabolite levels in foot muscle and digestive gland tissues demonstrated that glycolytic control during early estivation was primarily vested in pyruvate kinase. Relative to control values, the mass action ratio (MAR) of this reaction decreased by a factor of 4 in the foot muscle and by a factor of 2.7 in the digestive gland, reflecting inhibition of this enzyme in both tissues. No other glycolytic reaction appeared to be inhibited. Exposure of non-estivating snails to artificial hypercapnia resulted in extracellular acid-base conditions similar to those seen during estivation and also promoted a reduction in respiration rate. However, the points of glycolytic control were different: artificial hypercapnia resulted in inhibition of phosphofructokinase in foot muscle and hexokinase in digestive gland. Furthermore, elevated ambient CO2 had no effect on the MAR of the pyruvate kinase reaction in non-estivating snails. These results suggest that the action of extracellular acid-base variables alone cannot fully explain the down-regulation of glycolysis which occurs during estivation in this land snail. © 1991 Springer-Verlag.