Key result
The cardiac muscle of the black widow spider Latrodectus mactans features striated muscle with intercalated discs containing gap junctions and desmosomes, and is neurogenically driven by multiple axons.
Why the study?
Although arthropod heart muscle has been estimated to be less efficient than vertebrate muscle, certain arthropods display superior characteristics, prompting an investigation into the fine structural features of intercalated discs and cardiac junctions in the black widow spider.
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No clinical implications for human hearts; leaves open comparative ultrastructure of arthropod cardiac junctions.
Arthropods have an open circulatory system with a simple tubular heart, so it has been estimated that the contractile pumping structure of the cardiac muscle will be less efficient than that of vertebrates. Nevertheless, certain arthropods are known to have far superior properties and characteristics than vertebrates, so we investigated the fine structural features of intercalated discs and cardiac junctions of cardiac muscle cells in the black widow spider Latrodectus mactans. Characteristically, the spider cardiac muscle has typical striated features and represents a functional syncytium that supports multiple connections to adjacent cells by intercalated discs. Histologically, the boundary lamina of each sarcolemma connects to the basement membrane to form an elastic sheath, and the extracellular matrix allows the cells to be anchored to other tissues. Since the intercalated disc is also part of sarcolemma, it contains gap junctions for depolarization and desmosomes that keep the fibers together during cardiac muscle contraction. Furthermore, fascia adherens and macula adherens (desmosomes) were also identified as cell junctions in both sarcolemma and intercalated discs. To enable the coordinated heartbeat of the cardiac muscle, the muscle fibers have neuronal innervations by multiple axons from the motor ganglion.
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Sun et al. (2020) studied this question. The cardiac muscle of the black widow spider Latrodectus mactans features striated muscle with intercalated discs containing gap junctions and desmosomes, and is neurogenically driven by multiple axons.
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