Developmental changes in the plasma membrane of gizzard smooth muscle of the chicken. A freeze-fracture study.

Plasma membranes of chicken gizzard at embryonic, early post-hatching and adult stages were examined by the freeze-fracture technique and developmental changes in surface caveolae, intramembranous particles and gap junctions were found. The number of caveolae increased linearly during 11 to 21 days embryonic stages, from 1 to 7/micrometers2 of membrane surface, and their arrangement into subparallel bands took place in the early post-hatching period. The average density of caveolae at this time was 14/micrometers2, which increased in the adult to about 37/micrometers2. The intramembranous particles in embryonic muscle membranes were uniformly distributed with a P-face density of about 1000 particles/micrometers2; at 5 days post-hatching and at adult stages this particle density in the caveolar band regions increased to about 1700/micrometers2 and 2000/micrometers2, respectively. The gap junctions in contained embryonic gizzard consisted of only 12-14 particles, in the 5-days old chick they contained up to 200 particles, whereas in the adult up to 1000 particles were seen. The gizzard muscle shows the most striking developmental changes during the early post-hatching period and offers a good system for studies of membrane differentiation.