Heart gap junction preparations reveal hemiplaques by atomic force microscopy.
Lal, R., S. A. John, D. W. Laird, and M. F. Arnsdorf.
Department of Medicine, University of Chicago, Chicago, IL 60637,
Department of Medicine UCLA, Los Angeles, CA 90024, Department of Anatomy and
Cell Biology, McGill University, Montreal, Canada
APStracts 2:0033C, 1995.
Current structural models of gap junctions indicate two apposed plasma
membranes with hexagonally packed hemichannels in each membrane aligning end
to end. These channels connect the cytoplasms of contacting cells. Images of
isolated rat heart gap junctions have been made with the atomic force
microscope in aqueous media. We show that native cardiac gap junctions have a
thickness of 25 +/- 0.6 nm. This decreases to 17 nm when they are treated with
trypsin: known to remove some cytoplasmic components of Connexin-43. Imaging
shows subunits with a center to center spacing of 9-10 nm and long range
hexagonal packing, measurements in agreement with studies using freeze
fracture and negative stain electron microscopy. In addition to gap junctions
we imaged structures which had all the characteristics of native gap
junctions except their thickness was limited to 9-11 nm. They also show long
range hexagonal packing and center to center spacing of 9-10 nm. These
structures decrease in thickness, to 6-9 nm, when treated with trypsin. We
have called these structures hemiplaques. They appear to be present
endogenously in the preparation as we have ruled out them being an artifact
of imaging by AFM. However, it remains to be determined if they are a
consequence of the procedure used in isolating gap junctions or a possible
intermediary in gap junction formation.
Received 8 June 1994; accepted in final form 28 October 1994
APS Manuscript Number C0317-4.
Article publication pending Am. J. Physiol. (Cell Physiology).
ISSN 1080-4757 Copyright 1994 The American Physiological Society.
Published in APStracts on 27 February 1995.