[Functional status and ultrastructure of the smooth muscle coat of arteries].

The ultrastructure of smooth-muscle sheath of the rabbit ear artery was studied in situ with the blood flow preserved both in contracted and in relaxed states. In the latter state a decrease in the volume of smooth-muscle cells and a relative increase of interfellular space were revealed. These findings suggest a redistribution of fluid in the artery wall during contraction and relaxation which can be important for transport of substances in the vascular wall. In relaxation of smooth-muscle cell such phenomena as desaggregation of thick myosin myofilaments, considerable reduction of the micropinocytose apparatus, shifting of contractile elements to the cell's central zone, partial discomplexation of the endoplasmatic reticulum, were revealed. Possible mechanisms of the ultrastructural changes and their functional role are discussed.