The Ca2+-dependent dissociation of [3H]dopamine bound to an acidic glycoprotein present in the synaptosomal cytoplasm of rat brain.
The interaction of [3H]dopamine with acidic proteins present in the synaptosomal cytoplasm of rat brain was studied from the point of view of Ca2+-dependent release of dopamine as a neurotransmitter. Some of the proteins were glycoproteins and showed various affinities for [3H]dopamine. [3H]Dopamine bound to an acidic protein with a molecular weight of about 45,000 daltons became reversibly unbound in the presence of Ca2+, while that bound to other proteins did not. The amount of [3H]dopamine bound to the 45,000-dalton glycoprotein was 48.7 pmol/mg protein, and the Ca2+-concentration required to release half of the bound dopamine was found to be 0.2 to 0.25 mM under the experimental conditions. However, Ca2+ did not bind to any component of the acidic proteins and it is likely that the cation dissociates the bound dopamine by forming a complex with it. No calmodulin (-like protein) was detectable among the acidic proteins. Possible roles of the glycoproteins are discussed in relation to a Ca2+-dependent mechanism of neurotransmitter release.
D000818:Animals; D001921:Brain / Q000378:metabolism*; D002118:Calcium / Q000494:pharmacology*; D003593:Cytoplasm / Q000378:metabolism; D004298:Dopamine / Q000378:metabolism*; D006023:Glycoproteins / Q000302:isolation & purification / Q000378:metabolism*; D008297:Male; D008970:Molecular Weight; D011485:Protein Binding; D051381:Rats; D011919:Rats, Inbred Strains; D013574:Synaptosomes / Q000378:metabolism*; D014316:Tritium
D006023:Glycoproteins; D014316:Tritium; D002118:Calcium; D004298:Dopamine