Plasma membrane homeostatic function

Each cell is surrounded by a plasma membrane that separates the cytoplasmic contents of the cell, or the intracellular fluid, from the fluid outside the cell, the extracellular fluid. An important homeostatic function of this plasma membrane is to serve as a permeability barrier that insulates or protects the cytoplasm from immediate changes in the surrounding environment. Furthermore, it allows the cell to maintain a cytoplasmic composition very different from that of the extracellular fluid the functions of neurons and muscle cells depend on this difference. The plasma membrane also contains many enzymes and other components such as antigens and receptors that allow cells to interact with other cells, neurotransmitters, blood-borne substances such as hormones, and various other chemical substances, such as drugs. 

Relatively little attention has been given to another important aspect of transporter function. Several lines of evidence have suggested that drugs affecting monoamine transporters can significantly modulate presynaptic neuronal homeostasis (17-22). However, until genetic animal models with targeted disruption of these transporters became available (23-25), this homeostatic role of plasma membrane transporters was not fully appreciated. 

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