Date of Award

1983

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Abstract

Freshwater bivalves increase Na influx when the mussels were injected with dibutyryl cAMP, serotonin (5-HT), or 5-HT (10('-4) M/l) was added to the bath; a response similar to a sodium depleted mussel. Serotonin stimulated Na influx kinetics (K(,m) = 0.09 mM/l and J(,max) = 4.33 (mu)eq (g dry tissue (.) hr)('-1) were similar to Na depleted mussels. Stimulated Na influx (by dibutyryl cAMP or 5-HT) was inhibited by amiloride (5 x 10('-4) M/l) and the amiloride inhibition was reversible. Serotonin also changes water balance; the 5-HT stimulated mussels gain 0.36 ml H(,2)O (g dry tissue (.) hr)('-1) above controls. Serotonin stimulation of the Na influx was observed to be dose dependent and the net Na flux was related to endogenous gill cAMP content. Cyclic AMP in isolated gills incubated in pondwater containing 10('-4) M/l 5-HT was highest by 1 min, then declined over 20 min, however the elevated cAMP content was maintained constant with 1.0 mM/l theophylline included in the pondwater. Isolated gills cAMP content increased with the addition of 5-HT, dopamine, norepinephrine and epinephrine (10('-4) M/l) in pondwater. Adenylate cyclase (AC) activity was present in freshwater bivalve gill tissue and was stimulated by 5-HT (Half maximal, 3 (mu)M/l) and dopamine (half maximal, 1 (mu)M/l). Cyproheptadine inhibited the 5-HT dependent increase in AC activity and chlorpromazine inhibited dopamine stimulated AC activity. Prostaglandin E(,2), an inhibitor of Na transport in mussels, did not affect mussel gill AC activity. Gill AC activity was variable and could be inversely related to endogenous calcium with the greatest calcium effect on monoamine (5-HT and dopamine) sensitive AC activity. Crude homogenate pellet AC activity was significantly lower than purified pellet. Exogenous calcium (2.5 mM/l) inhibited monoamine stimulated AC activity in the purified pellet about 50%. Phosphodiesterase and nonspecific phosphatase were highest in the supernatant. The data indicate Na regulation in mussels is dependent on a serotonin stimulated cAMP enzyme system.

Pages

122

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