The effect of formaldehyde exposure on the transmembrane distribution of free amino acids in muscles of Mytilus edulis

Free amino acids in the posterior adductor muscle of mussels (Mytilus edulis) occur in a high-energy gradient group, with energy gradients of 15­18 kJ mol-1 (aspartate, beta-alanine, glycine, taurine and threonine), and a low-energy gradient group, with energy gradients around 12 kJ mol-1 (the rest of the amino acids). Two of the amino acids, glycine and taurine, are present at intracellular concentrations of 100­150 mmol kg-1, while the other amino acids occur at concentrations below 50 mmol kg-1. Exposure of mussels to formaldehyde causes a marked influx of Na+ into the muscle cells and an increase in cellular water content. The Na+ gradient, which provides the energy for the cellular accumulation of free amino acids, is reduced. The drop in the Na+ gradient is accompanied by a nearly proportional reduction in the energy gradients of all amino acids in the high-energy gradient group and a 150 mmol kg-1 reduction in the total intracellular concentration of free amino acids. Most of this reduction is made up by the Na+-dependent amino acids aspartate, glycine and threonine, the concentrations of which are reduced by about 120 mmol kg-1. The transmembrane distribution of the low-energy gradient amino acids seems to be independent of the Na+ gradient, and these amino acids display only moderate reductions in their intracellular concentrations when the Na+ gradient is reduced. The reduction in the concentrations of the free amino acids appears to be a volume-regulatory response, serving to bring the cell volume back to its optimal level after the formaldehyde-induced Na+ influx has caused a cellular swelling. The basis of these differences in Na+-dependence is discussed. Taurine, which is the quantitatively dominating organic solute and an important volume-regulatory osmolyte in mussels, does not take part in the volume-regulatory response. This may be due the role of taurine in the protection against potentially toxic Ca2+, which enters the cells in large quantities when mussels are exposed to formaldehyde.

Pollutant-induced depression of the transmembrane sodium gradient in muscles of mussels.

This study deals with the effects of chemical pollutants on the transmembrane potential difference for sodium (delta mu Na) in smooth muscle cells of Mytilus edulis. A method for indirect determination of extracellular space, intracellular ion concentrations and delta mu Na has been developed and is applied in the investigations. The determination is based on concentration data from haemolymph and muscle tissue samples. The precision of the method used was tested by direct measurements of the apparent intracellular concentration of sodium and the membrane potential. On the basis of these tests, the method was evaluated as reasonably good. The method was used to study the sensitivity of the transmembrane delta mu Na in Mytilus edulis to 96 h exposures to various sublethal concentrations of formaldehyde, methanol and mercury. Both formaldehyde and mercury induced a depression of delta mu Na. The observed depressions could be ascribed to a change in both the electrogenic and the chemical components of delta mu Na. A depression of delta mu Na was associated with subsequent clinical injury and death. Methanol did not cause death or any changes in delta mu Na. Because of the observed correlation between depression of delta mu Na and clinical injury, delta mu Na is suggested to have a potential as an indicator of toxicity.

Physiological parameters in ecotoxicology.

1. Regulated physiological parameters are normally maintained at a constant level by regulatory mechanisms. Acute toxic effects develop whenever a pollutant causes a regulated parameter to be displaced beyond tolerated limits, and thus, regulated parameters may be convenient toxicity parameters. The present study indicates that delta mu Na+ across the adductor muscle membrane of Mytilus edulis is a regulated parameter, and that injuries develop whenever this parameter drops below -700 J/mole. 2. Regulatory physiological parameters may display quick and substantial changes when regulatory mechanisms are activated to counteract variations in the regulated parameters. Thus, regulatory parameters may be used as sensitive alarm parameters in environmental monitoring. The present results indicate that the phosphate index [(ATP x P-arginine)/(Pi)2], metabolic rate and strombine may be used as alarm parameters. 3. The combined response of all parameters may provide a pollutant-specific fingerprint in environmental monitoring.

The effects of organic and inorganic pollutants on intracellular phosphate compounds in blue mussels (Mytilus edulis).

1. The effects of sublethal concentrations of organic and inorganic pollutants on intracellular energy-rich phosphates in blue mussels, Mytilus edulis, were investigated by in vivo 31P-NMR. 2. Formaldehyde (30 and 10 mg/l), phenol, pyridine, mercury and cadmium gave marked reductions in phosphoarginine and, in some cases, the ATP amounts. The reduction in high-energy phosphate was accompanied by an increase in inorganic phosphate in all groups. 3. A "phosphorus index", the product of the ratios between phosphoarginine and inorganic phosphate, and ATP and inorganic phosphate, is suggested, which might serve as an early warning ("alarm") parameter in environmental monitoring. 4. Diversity in the responses to different pollutants make phosphorus compounds in M. edulis also an interesting element in a finger print parameter system designed to distinguish between pollutants in the marine environment.