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Calcium and small organic molecules (e.g., tyrosine, MW 181 Da) introduced into the extrapallial fluid (EPF) of the quahog Mercenaria mercenaria exhibit rapid fluxes across the outer mantle epithelium and are distributed throughout the circulatory system within 3 h. Larger molecules (e.g., bovine serum albumin, MW 66,000 Da) are less readily exchanged between EPF and blood. The protein compositions of blood plasma and EPF are different, with at least seven protein bands expressed more prominently in the EPF. Equilibrium dialysis experiments reveal that Ca2+ constitutes only 2% of the total Ca in plasma; most of the Ca (85%) is bound to macromolecules, and the remaining 13% is present as dialyzable low molecular weight moieties. This distribution cannot be explained by speciation of inorganic Ca alone, since the MINTEQA2 equilibrium speciation model predicts that 79%-86% of the Ca should be present as Ca2+, with the remainder as CaSO4 (20%-13%). However, inclusion of a weakly Ca-binding organic molecule (log10 Ka approximately 2 M-1) into MINTEQA2 could fully reconcile modeling with experimental measurements. Results suggest that calcium transport in blood plasma and EPF is mediated by a suite of proteins and small organic ligands with a low affinity for Ca.

Cadmium-binding parameters (conditional stability constants and carrying capacities) of Mytilus edulis blood plasma histidine-rich glycoprotein (HRG) were investigated by potentiometric titrations using a Cd ion-specific electrode. Titration data were applied to a single-component complexation model and expressed as Scatchard plots that were analyzed using the graphical curve peeling method and the algebraic statistical mechanical method. These sets of binding parameters, derived for the purified HRG, were subsequently entered into the geochemical speciation model MINTEQA2 and then used to simulate the experimental titration, thereby determining which set of log K and CL values best represented the titration data. The Cd binding to HRG was best described by a two-class model with log K values of 7.65 +/- 0.10 and 5.41 +/- 0.06 M-1 and carrying capacities of 6.0 +/- 1.2 and 9.5 +/- 0.4 sites/molecule, respectively. At concentration of total Cd measured in the blood plasma of field-collected mussels (< or = 2 x 10(-7) M), plasma Cd speciation would be dominated by the strong affinity sites of HRG (> 93.5% of total Cd binds to HRG), whereas HRG itself would only be 0.05% saturated with Cd, indicating a high-capacity, apparently nonsaturable Cd transport system.

A 46-year-old white male diagnosed with systemic lupus erythematosus (SLE) and antiphospholipid syndrome (APS) was seen for audiological testing 15 minutes following a sudden onset hearing loss in the right ear. The test battery included pure-tone audiometry, word-recognition testing, speech-recognition threshold (SRT) testing, immittance testing, and distortion-product otoacoustic emissions (DPOAE) testing. Testing revealed a sensorineural hearing loss in the right ear. Shortly after testing, the patient indicated that his condition had improved. Testing was repeated, and the second round of tests revealed normal hearing in both ears. Four days later, a follow-up test again indicated normal hearing in both ears. Possible connections of this brief occurrence of idiopathic hearing loss with the patient's medical conditions are discussed. Specifically, symptoms were consistent with a transient ischemic attack (TIA) affecting his right cochlea in the stria vascularis region, resulting in a temporary, sensorineural hearing loss. No residual effects were observed clinically.

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