Diurnal rhythms of sodium transport in the freshwater mussel

Sodium and chloride concentrations in the blood of pondwater acclimated Carunculina texasensis on a 12 h light (L): 12 h dark (D) photoperiod, undergo daily oscillations of 1 to 2 mmol/L. Changes in the active transport rate of Na are responsible for the changes in the blood sodium levels over the 24-h period. During the photophase, the blood level of Na and Cl is at a nadir and the clams are losing Na (net flux (Jn) = −0.36 μ mol/g dry tissue∙h−1) due to a depressed Na influx (Ji = 0.30 μ mol/g dry tissue∙h−1). The opposite response is observed during the scotophase; the blood concentration is significantly increased and the mussels are gaining sodium (Jn = 0.36 μ mol/g dry tissue∙h−1) by increasing the influx of Na (Ji = 0.79 μ mol/g dry tissue∙h−1).