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| Untersuchte Arbeit: Seite: 10, Zeilen: 1-21 |
Quelle: Herreras et al 1994 Seite(n): 7087, 7097, Zeilen: 7087: r.col: 27ff; 7097: l.col: 2ff |
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| [Among antecedents heralding the onset of SD that have been reported, are] a slight increase of extracellular potassium, a small positive shift preceding the fast negative shift of the extracellular potential and several types of fast field activity including a short burst of action potentials or intense synaptic noise (Leao, 1944; Higashida et al., 1974). Even a silence of spontaneous or evoked activity has occasionally been described prior to other signs (Higashida et al., 1974). Not all of these early signs are obligatory prodromals of the large, accelerating, regenerative depolarization that is typical of the process.
Even though the discharge of impulses is not required for the initiation or the propagation of SD, the impulse shower does regularly appear at its beginning. The mechanism that gives rise to the impulse discharge may well have a key role in the evolution of SD. The widely spread synchronization seems best explained by electrical continuity that could be provided by gap junctions. Effective communication by way of quasi-syncytial nets has been demonstrated in other systems, for example in the spread of so-called calcium waves in cell cultures (Cornell-Bell et al., 1990). Patent gap junctions may provide a path not only for electric current and for ions but also for intracellular “second” messengers and other active ingredients in cytosol. SD has frequently been interpreted as a diffusion-reaction process whose velocity of spread is governed by the rate of the reaction, which could involve the release of some substance from cells that then acted on the cell membrane of adjacent cells. As there are reasons for doubting a decisive role of either K or of glutamate, we are proposing an alternative hypothesis, involving the exchange of chemical signals not through the interstitial space but by way of gap junctions. The autocatalytic reaction so initiated would alter the membrane from the inside, instead of acting on receptors on the outside. |
Among antecedents heralding the onset of SD that have been reported, are a slight increase of extracellular potassium ([K+]0), a small positive shift preceding the fast negative shift of the extracellular potential (ΔV0) (Marshall, 1959) and several types of fast field activity including a short burst of action potentials or intense synaptic noise (Leao, 1944; Grafstein 1956; Rosenblueth and Garcia-Ramos, 1966; Ichijo and Ochs, 1970; Higashida et al., 1974; Somjen and Aitken, 1984; Haglund and Schwartzkroin, 1990; Herreras and Somjen, 1993a). Even a silence of spontaneous or evoked activity has occasionally been described prior to other signs (Grafstein, 1956; Morlock et al., 1964; Muiioz, 1970; Higashida et al., 1974). Not all of these early signs are obligatory prodromals of the large, accelerating, regenerative depolarization that is typical of the process.
[page 7097] Even though the discharge of impulses is not required for the initiation or the propagation of SD, the impulse shower does regularly appear at its beginning. The mechanism that gives rise to the impulse discharge may well have a key role in the evolution of SD. The widely spread synchronization seems best explained by electrical continuity that could be provided by gap junctions. Effective communication by way of quasi-syncytial nets has been demonstrated in other systems, for example in the spread of so-called calcium waves in cell cultures (Cornell-Bell et al., 1990; Dani et al., 1992; Finkbeiner, 1992). Patent gap junctions may provide a path not only for electric current and for ions but also for intracellular “second” messengers and other active ingredients in cytosol. SD has frequently been interpreted as a diffusion-reaction process whose velocity of spread is governed by the rate of the reaction, which could involve the release of some substance from cells that then acted on the cell membrane of adjacent cells. As there are reasons for doubting a decisive role of either K or of glutamate, we are proposing an alternative hypothesis, involving the exchange of chemical signals not through the interstitial space but by way of gap junctions. The autocatalytic reaction so initiated would alter the membrane from the inside, instead of acting on receptors on the outside. |
The source is not mentioned. |
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