Regulation of intracellular membrane interactions: Recent progress in the field of neurotransmitter release

Maintenance of compartmental independence and diversity is part of the blue print of the eukaryotic cell. The molecular composition of every organelle membrane is custom tailored to fulfill its unique tasks. it is retained by strict sorting and directional transport of newly synthesized cellular comp onents by the use of specific transport vesicles. Temporally and spatially controlled membrane fission and fusion steps thus represent the basic proce ss for delivery of both, membrane-bound and soluble components to their app ropriate destination. This process is fundamental to cell growth, organelle inheritance during cell division, uptake and intracellular transport of me mbrane-bound and soluble molecules, and neuronal communication. The tatter process has become one of the best studied examples in terms of regulatory mechanisms of membrane interactions. It has been dissected into the stages of transmitter vesicle docking, priming, and fusion: Specificity of membran e interactions depends on interactions between sets of organelle-specific m embrane proteins. Priming of the secretory apparatus is an ATP-dependent pr ocess involving proteins and membrane phospholipids. Release of vesicle con tent is triggered by a rise in intracellular free Ca2+ levels that relieves a block previously established between the membranes poised to fuse. Neuro transmitter release is a paradigm of highly regulated intracellular membran e interaction and molecular mechanisms for this phenomenon begin to be deli neated.. Cell. Biochem. Suppls. 30/31:103-110, 1998. (C) 1998 Wiley-Liss, I nc.