Figure 8.
Schema of myocardial adrenergic neuronal terminals Figure A shows the schematic representation of myocardial adrenergic neuronal terminals and Figure B shows the chemical structure of each tracer. MIBG is actively taken up into sympathetic nerves through the uptake-1 mechanism and then stored in the synaptic vesicle in a manner similar to that for norepinephrine (NE). Nerve stimulation releases MIBG and NE into the synaptic cleft through exocytosis. MIBG does not bind to the postsynaptic receptor and is not metabolized by monoamine oxidase (MAO) or catechol-O-methyltransferase (COMT). Most of the released MIBG undergoes reuptake through the uptake-1 mechanism, and the remaining MIBG goes into the blood (spillover). 123 I-MIBG, m-[123I]iodobenzylguanidine; 11 C-HED, 11C-hydroxyephedrine; DAG, diacylglycerol; AR, adrenergic receptor;Gq, phospholipase C-coupled Gq-protein; Gs, phospholipase C-coupled Gs-protein; ATP, adenosine triphosphate; cAMP, cyclic adenosine monophosphate; IP 2, inositol bisphosphate; PIP 2, phosphatidylinositol biphosphate