Changes in dopamine uptake and developmental effects of dopamine receptor inactivation in the sea urchin

[3H]-dopamine ([3H]-DA) uptake was measured in the presence or absence of the catecholamine uptake inhibitor nomifensine in both unfertilized and fertilized eggs. Specific [3H]-DA uptake depended on time and [3H]-DA concentration; it was high in unfertilized eggs, declined 20-30 min after fertilization, and rose again during cleavage. Irreversible inactivation of dopamine receptors by N-ethoxycarbonyl-2-ethoxy-1,2-dihydroquinoline (EEDQ) resulted in a complete loss of sensitivity of egg adenylate cyclase to dopamine stimulation. In fertilized eggs treated with EEDQ for 1 hr, restoration of adenylate cyclase activity sensitive to dopamine stimulation could be observed 4 hr after the end of treatment, thus suggesting the appearance of new dopamine receptors in cleaving eggs. Short-term EEDQ treatment on unfertilized eggs, although not impairing fertilization, resulted in cleavage inhibition; the same treatment carried out soon after fertilization, on the other hand, elicited no effect on development. On the contrary, in embryos subjected to continuous treatment with EEDQ, development was impaired independent of the stage at which the treatment was started.