POTASSIUM TRANSPORT IN THE FRESHWATER BIVALVE DREISSENA POLYMORPHA

摘要

Potassium transport and blood ion composition were examined in the freshwater bivalve Dreissena polymorpha. Animals acclimated to artificial pondwater (APW, [K+]=0.05 mmol l(-1)) for 4 weeks gradually lost Na+ and Cl-, but the blood K+ concentration remained constant near 0.5 mmol l(-1), Blood [K+] in D. polymorpha declined by 41 % after 1 week of exposure to K+-free APW. Conversely, blood [K+] rose to 1.52+/-0.05 mmol l(-1) (mean +/- S.E.M.) 24 h after exposure to 0.5 mmol l(-1) K+ APW. Total tissue K+ content remained stable in animals maintained in APW, but fell significantly in animals exposed to K+-free APW for 2 weeks, The net K+ flux (J(net)) for animals incubated in APW, with an average K+ concentration of 0.07 mmol l(-1), was -0.27+/-0.06 mu equiv g(-1) dry tissue h(-1), significantly different from the value of 0.50+/-0.08 mu equiv g(-1) dry tissue h(-1) for animals transferred to 0.30 mmol l(-1) K+ APW. A transepithelial membrane potential of -3.6+/-0.7 mV (blood negative compared with the bathing medium) was measured in APW-acclimated mussels, Potassium influx was measured with K-42 and displayed Michaelis-Menten saturation kinetics at dilute K+ concentrations, The K-m was 0.084+/-0.054 mmol l(-1) and the J(max) was 1.74+/-0.39 mu equiv g(-1) dry tissue h(-1), Both the K-m and J(max) for animals exposed to K+-free APW for 7 days were unchanged, Using Rb-86, qualitatively similar transport characteristics were observed for animals incubated in K+-free, Rb+ APW, but the 22 day K+ depletion time significantly increased J(max) D. polymorpha compensated for changes in the ionic composition of the acclimation medium by tolerating alterations in blood solute composition and adjusting ion transport rates. [References: 26]