INVESTIGATIONS INTO THE BIOCHEMICAL BASIS OF NEUROMODULATION BY 2-PHENYLETHYLAMINE - EFFECT ON MICROTUBULE PROTEIN

In order to understand the role of 2-phenylethylamine (PE) on neuronal responses, membrane changes have been studied using ESR probes. We re port that the anticipated change in lipid membrane fluidity generally implicated in signal transduction has not been observed when PE is add ed to synaptosomes. As cytoskeletal architecture of presynaptic termin als appears to be involved in synaptic transmission, we non-specifical ly labeled synaptosomal membrane proteins with the sulfhydryl spin pro be N-(2,2,6,6-tetramethyl-piperidine-1-oxyl-4-yl) maleimide (4-MAL-TEM PO). The addition of 2-phenylethylamine was found to induce conformati onal changes, in decreasing the ratio of weakly to strongly immobilize d spin label (W/S) to 65% of the control. Of the membrane proteins lab eled, 70-90% of the 4-MAL-TEMPO is covalently incorporated into cytosk eletal proteins. In isolated synaptosomes, incorporated with spin-labe led tubulin, the addition of PE reduced the W/S ratio to 51.6% of that obtained for polymerized microtubules. In vitro, PE reduced tau(R) of polymerized microtubules by 37%. We propose that the PE interaction w ith tubulin changes microtubule dynamics which may lead to its neuromo dulatory action. The state of microtubular assembly can modulate the r esponsiveness of second messengers in the cell to the effect of stimul atory agents. The nature and physiological significance of PE interact ion with tubulin is currently under investigation.