Summary
The caprine sinoatrial node (SAN) and atrioventricular node (AVN) were studied by freeze-fracture techniques, and their nexus or gap junction structure were compared with that of ordinary atrial and ventricular muscle cells. The general features of the nexus in both the SAN and AVN were essentially identical. Approximately two-thirds of the nexuses observed in the nodal cells consisted of typical macular arrangements of nexal particles, and the remaining third, of atypical configurations of either circular arrangements or linear arrays of particles in continuity with the macular nexuses. Such atypical nexuses were never observed in the ordinary adult myocardial cells. Quantitative analysis revealed that all of the nexuses in the nodal cells measured, were less than 0.1 μm2, whereas the majority of the nexuses in ordinary myocardial cells (64% in the atrium and 76% in the ventricle) were larger than 0.1 μm2. No significant differences in diameter and center-to-center distance of nexal particle were found between the nodal cells and ordinary myocardial cells.
This is a preview of subscription content, log in via an institution to check access.
Similar content being viewed by others
References
Akester AR (1981) Intercalated discs, nexuses, sarcoplasmic reticulum and transitional cells in the heart of adult domestic fowl (Gallus gallus domesticus). J Anat 133:161–179
Bhatnagar KP, Spoonamore BA (1979) Ultrastructure of the atrioventricular node of the big brown bat, Eptecicus fucus. Acta Ant 105:157–180
Dahl G, Isenberg G (1980) Decoupling of heart muscle cells: Correlation with increased cytoplasmic calcium activity and with changes of nexus ultrastructure. J Membr Biol 53:63–75
Délèze J, Hervé JC (1983) Effect of several uncouplers of cell-to-cell communication on gap junction morphology in mammalian heart. J Membr Biol 74:203–215
De Mello WC (1982) Cell-to-cell communications in heart and other tissues. Prog Biophys Mol Biol 39:147–182
Green CR, Severs NJ (1984) Connexon rearrangement in cardiac gap junctions: Evidence for cytoskeletal control? Cell Tissue Res 237:185–186
Gros D, Challice CE (1975) Early development of gap junctions between the mouse embryonic myocardial cells. A freeze-etching study. Experientia 32:996–998
Gros D, Mocquard JP, Challice CE, Schrevel J (1978) Formation and growth of gap junctions in mouse myocardium during ontogenesis. A freeze-fracture study. J Cell Sci 30:45–61
Gros D, Mocquard JP, Challice CE, Schrevel J (1979) Formation and growth of gap junctions in mouse myocardium during ontogenesis. Quantitative data and their implications on the development of intercellular communication. J Mol Cell Cardiol 11:543–554
Hellenbrecht D, Lemmer B, Wiethold G, Grobecker H (1973) Measurement of hydrophobicity, surface activity, local anaesthesia, and myocardial conduction velocity as quantitative parameters of the non-specific membrane affinity of nine β-adrenergic blocking agents. Naunyn Schmiedebergs Arch Pharmacol 277:211–226
Katz AM (1977) Physiology of the heart. Raven Press, New York, pp 257–292
Kensler RW, Brink P, Dewey MM (1977) Nexus of frog ventricle. J Cell Biol 73:768–781
Larsen WJ (1977) Structural diversity of gap junctions. A review. Tissue Cell 9:373–349
Masson-Pévet M, Bleeker WK, Gros D (1979) The plasma membrane of leading pacemaker cells in the rabbit sinus node. A qualitative and quantitative ultrastructural analysis. Circ Res 45:621–629
Mazet F (1977) Freeze-fracture studies of gap junctions in the developing and adult amphibian cardiac muscle. Dev Biol 60:139–152
Mazet F, Cartaud J (1976) Freeze-fracture studies of frog atrial fibres. J Cell Sci 22:427–434
McNutt NS (1975) Ultrastructure of the myocardial sarcolemma. Circ Res 37:1–13
McNutt NS, Weinstein RS (1970) The ultrastructure of the nexus. A correlated thin-section and freeze-cleave study. J Cell Biol 47:666–688
Schiebler TH, Doerr W (1963) Orthologie des Reizleitungssystems. In: Bargmann W, Doerr W (eds) Das Herz des Menschen. Bd I. Georg Thiem Stuttgart, pp 169–227
Shibata Y, Page E (1981) Gap junctional structure in intact and cut sheep cardiac Purkinje fibers: a freeze-fracture study of Ca2+-induced resealing. J Ultrastruct Res 75:195–204
Shibata Y, Yamamoto T (1979) A Freeze-fracture study of gap junctions in vertebrate cardiac muscle cells. J Ultrastruct Res 67:79–88
Shibata Y, Nakata K, Page E (1980) Ultrastructural changes during development of gap junctions in rabbit left ventricular myocardial cells. J Ultrastruct Res 71:258–271
Sugi Y, Hirakow R (1983) Ultrastructural differentiation of the caprine cardiac muscle cells: Nodal cells in comparison with ordinary myocardial cells. J Electron Microsc 32:262
Tranum-Jensen J (1978) The fine structure of the sinus node: a survey. In: Bonke FIM (ed) The sinus node. Martinus Nijihoff Medical Division, Hague Boston London, pp 149–165
Truex RC, Smythe MQ (1965) Comparative morphology of the cardiac conduction tissue in animals. Ann NY Acad Sci 127:19–33
Virágh S, Challice CE (1973) The impulse generation and conduction system of the heart. In: Challice CE, Virágh S (eds) Ultra-structure of the mammalian heart. Academic Press, New York London, pp 43–89
Williams EH, DeHaan RL (1981) Electric coupling among heart cells in the absence of ultrastructurally defined gap junctions. J Membr Biol 60:237–248
Author information
Authors and Affiliations
Rights and permissions
About this article
Cite this article
Sugi, Y., Hirakow, R. Freeze-fracture studies of the sinoatrial and atrioventricular nodes of the caprine heart, with special reference to the nexus. Cell Tissue Res. 245, 273–279 (1986). https://doi.org/10.1007/BF00213932
Accepted:
Issue Date:
DOI: https://doi.org/10.1007/BF00213932