AJP - Cell Physiology, Vol 263, Issue 5 C959-C977, Copyright © 1992 by American Physiological Society
Differences in gap junction channels between cardiac myocytes, fibroblasts, and heterologous pairs
M. B. Rook, A. C. van Ginneken, B. de Jonge, A. el Aoumari, D. Gros and H. J. Jongsma
Department of Physiology, University of Amsterdam, The Netherlands.
Cultures of neonatal rat heart cells contain predominantly myocytes and
fibroblastic cells. Most abundant are groups of synchronously contracting
myocytes, which are electrically well coupled through large gap junctions.
Cardiac fibroblasts may be electrically coupled to each other and to
adjacent myocytes, be it with low intercellular conductances. Nevertheless,
synchronously beating myocytes interconnected via a fibroblast were
present, demonstrating that nonexcitable cardiac cells are capable of
passive impulse conduction. In fibroblast pairs as well as in
myocyte-fibroblast cell pairs, no sensitivity to junctional voltage could
be detected when transjunctional conductance was > 1-2 nS. However, in
pairs coupled by a conductance of < 1 nS, complex voltage-dependent
gating was evident; gap junction channel open probability decreased with
increasing junctional voltage but a nongated residual conductance remained
at all voltages tested. Single gap junction channel conductance between
fibroblasts was approximately 21 pS, very similar to an approximately 18-pS
channel conductance that was found between myocytes next to the major
conductance of 43 pS. Single-channel conductance in heterologous
myocyte-fibroblast gap junctions was approximately 32 pS, which matches the
theoretical value of 29 pS for gap junction channels composed of a
fibroblast connexon and the major myocyte connexon. A site-directed
antibody against rat heart gap junction protein connexin43 recognized gap
junctions between neonatal cardiomyocytes, as demonstrated by
immunocytochemical labeling. In contrast, junctions between fibroblasts
showed no labeling, while in myocyte-fibroblast junctions labeling
occasionally was present. Our results suggest the existence of two gap
junction proteins between neonatal rat cardiocytes, connexin43 and another
yet unidentified connexin. An alternative explanation (cell-specific
regulation of the conductance of connexin43 channels) is discussed.
