In vitro cultivation of rabbit aortic media and the development of the cultures in relation to cellular heterogeneity.

Explants of rabbit aortic media were transferred to tissue culture and the development of the characteristic regions of the cultures was followed. With a new technique the explants were instantly immobilized in the culture flasks, by which the temporal development was strictly defined. The culture developed along the following four major lines: (1) cells migrated from the explant and some cells formed a network of large, attenuated cells, while other, smaller and poorly flattened cells formed clusters attached to the plastic or the network; (2) with continuing growth the network of larger and attenuated cells expanded, grew denser and formed the monolayered component of the culture; (3) multilayered thickenings formed at sites where poorly flattened small cells were numerous either within or at the outer margin of the monolayer or (4) at the margin of the explant where profuse emigration of cells had occurred. Thus, the development of the culture was dependent upon the growth behaviour and expansion of two subpopulation of cells. In the electron microscope the smaller, poorly flattened type of cell with multilayered growth pattern had features of a highly metabolically active cell and had numerous attachment sites of fibronexus type. The attenuated larger cell type growing as monolayers had very abundant microfilaments. The differences may reflect a functional segregation among different cell subpopulations in arterial smooth muscle tissue.