[Cell membrane receptors and intracellular signalling. Characterization in cultivated, contractile and endothelial...

Numerous hormones and mediators develop their effect via one or several specific receptors/subtypes. In glomerular endothelial cells (GEC), for example, the action of adenosine triphosphate is mediated by a novel nucleotide receptor. Since the latter is not found in large vessels, it is expected to play an important role in the regulation of the microcirculation. Substances with a very similar structure, such as vasopressin and oxytocin, can bind to the same receptor in vascular smooth muscle cells (VMC), although only the true agonist produces a maximum response. Following the binding of vasopressin to its specific V1-VP receptor, the ligand/receptor complex is internalized and processed within the cell. The freed receptor is then recycled to the cell membrane. This mechanism is responsible for the transient nature of vasopressin action. In VMC and the functionally similar contractile glomerular mesangial cells, vasopressin triggers intracellular signals, resulting in contraction. These signals may be enhanced or attenuated by numerous hormonal factors or mediators.