AJP - Heart and Circulatory Physiology, Vol 245, Issue 6 992-H997, Copyright © 1983 by American Physiological Society
P-face particle density of freeze-fractured vertebrate cardiac plasma membrane
L. Kordylewski, T. Karrison and E. Page
P-face particle density of freeze-fractured cardiac plasmalemma provides an
estimate of the total population of membrane channels, carriers, and
receptors that insert into or traverse unit area of lipid bilayer. We have
determined the size of this population of integral membrane protein
assemblies by counting the number of P-face particles per square micron of
plasmalemma in freeze-fractured hearts, using stereoimaged replicas tilted
with a goniometer stage in the electron microscope. Particle numbers per
square micron were 4,525 +/- 231, 4,799 +/- 235, 4,122 +/- 153, 4,281 +/-
218, and 5,848 +/- 300 for ventricular myocyte plasmalemmas of rat, rabbit,
8-day chick, adult chicken, and frog, respectively. These values are at
least two times greater than published values, in which stereo imaging was
not used. Published ligand-binding studies indicate that only the surface
density of the Na+-K+ pump sites can account for a significant fraction of
P-face particles; the rest so far lack functional correlates. Particle
density of frog heart plasmalemma significantly exceeded particle densities
of chicken and mammalian plasma membranes.
