Date of Award

1996

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

First Advisor

Thomas T. Dietz

Abstract

Corbicula fluminea (Muller) maintains hydromineral balance in dilute media by active transepithelial transport of Na and Cl. Cl uptake depended on external (Cl) and displayed saturable kinetics. The transport capacity in pondwater(PW)-acclimated animals was 7.00 $\pm$ 0.51 $\mu$eq(g dry tissue $\cdot$ h)$\sp{-1}$ and the transport affinity 0.21 $\pm$ 0.08 mM. Prolonged salt depletion increased Cl transport capacity without changing the affinity. In PW-acclimated C. fluminea, Na and Cl transport were independent, and were stimulated by serotonin. In salt depleted (SD)animals, Na transport was partially Cl-dependent but Cl transport was Na-independent. Acetazolamide increased Na and Cl efflux. Both serotonin and acetazolamide promoted the loss of titratable base. N, N$\sp\prime$-dicyclohexylcarbodiimide (DCCD) inhibited Na and Cl transport. The inhibition of Na transport by DCCD was Cl-dependent, but the inhibition of Cl transport was Na-independent. DCCD increased the loss of titratable base in Cl-free PW medium. 4,4$\sp\prime$-diisothiocyanostilbene-2,2$\sp\prime$-disulfonic acid decreased Cl influx and Na net flux. Furosemide inhibited Na and Cl transport in PW-acclimated animals. Exposure of C. fluminea to hyperosmotic nonelectrolytes resulted in an elevation of blood solutes due to dehydration followed by a precipitous decrease in blood Na and the accumulation of nonelectrolytes. Lanthanum was rarely observed to penetrate the paracellular spaces without hyperosmotic stress, but was observed in the paracellular junctional complexes between gill epithelial cells under hyperosmotic conditions. Longer exposure resulted in greater amounts of lanthanum precipitation in more locations compared to shorter exposure. Carunculina texasensis was able to maintain normal blood ion concentration for 8 h with minimal dehydration under hyperosmotic condition. Longer exposure caused a precipitous decrease in most blood solutes and an extensive accumulation of nonelectrolytes. More lanthanum was observed in the paracellular spaces of C. texasensis compared to C. fluminea for identical treatments. This study suggests that Na and Cl transport in C. fluminea are energized by a proton-pump. The entrance of Na is likely via an apical Na-conductive channel and Cl via an apical Cl/HCO$\sb3$ exchange pathway. It also suggests that under normal conditions the epithelium of C. fluminea is relatively "tight" and the paracellular pathway for solutes is insignificant.

ISBN

9780591133950

Pages

92

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