Recovery of ultrastructural changes accompanying caffeine contractures in isolated muscle fibres of the crayfish

Procaine effects on single sarcoplasmic reticulum Ca2+ release channels

The effects of the Ca(2+)-induced Ca2+ release blocker procaine on individual sarcoplasmic reticulum Ca2+ release channels have been examined in planar lipid bilayers. Procaine did not reduce the single channel conductance nor appreciably shorten the mean open times of the channel; rather, it increased the longest closed time. These results indicated that procaine interacted selectively with a closed state of the channel rather than with an open state. Gating of the sarcoplasmic reticulum Ca2+ release channel was described by a modified scheme of Ashley and Williams (1990. J. Gen. Physiol. 95:981-1005), including an additional long-lived closed state. Computer simulations determined that procaine was more likely to interact with this long-lived Ca(2+)-bound closed state of the channel rather than with other states of the channel. Simulations with the same model were also able to reproduce a prominent Ca(2+)-sensitive transition between "random" and "bursting" forms of gating of the channel, variations of which may account for "gearshift" behavior reported in studies with this and other single channels.

Calcium and magnesium contents and volume of the terminal cisternae in caffeine-treated skeletal muscle

(a) The effects of caffeine on the composition and volume of the terminal cisternae (TC) of the sarcoplasmic reticulum (SR) in frog skeletal muscle were determined with rapid freezing, electron microscopy, and electron probe analysis. (b) Caffeine (5 mM) released approximately 65% of the Ca content of the TC in 1 min and 84% after 3 min. The release of Ca from the TC was associated with a highly significant increase in its Mg content. This increase in Mg was not reduced by valinomycin. There was also a small increase in the K content of the TC at 1 min, although not after 3 min of caffeine contracture. (c) On the basis of the increase in Mg content during caffeine contracture and during tetanus (Somlyo, A. V., H. Gonzalez-Serratos, H. Shuman, G. McClellan, and A. P. Somlyo, 1981, J. Cell Biol., 90:577-594), we suggest that both mechanisms of Ca release are associated with an increase in the Ca and Mg permeability of the SR membranes, the two ions possibly moving through a common channel. (d) There was a significant increase in the P content of the TC during caffeine contracture, while in tetanized muscle (see reference above) there was no increase in the P content of the TC. (e) Mitochondrial Ca content was significantly increased (at 1 and at 3 min) during caffeine contracture. Valinomycin (5 microM) blocked this mitochondrial Ca uptake. (f) The sustained Ca release caused by caffeine in situ contrasts with the transient Ca release observed in studies of fragmented SR preparations, and could be explained by mediation of the caffeine-induced Ca release by a second messenger produced more readily in intact muscle than in isolated SR. (g) The TC were not swollen in rapidly frozen, caffeine-treated muscles, in contrast to the swelling of the TC observed in conventionally fixed, caffeine-treated preparation, the latter finding being in agreement with previous studies. (h) The fractional volume of the TC in rapidly frozen control (resting) frog semitendinosus muscles (approximately 2.1%) was less than the volume (approximately 2.5%) after glutaraldehyde-osmium fixation.

Calcium binding sites of hamster parasympathetic neurons

Sites of Ca localization in hamster submandibular ganglion cells have been studied by electron microscopy using the technique of Oschman et al. [11]. Electron-dense deposits, which we assume to contain Ca, are found: (i) on axonal plasma membranes; (ii) on the plasma membranes of neuron soma and its processes; (iii) on the membrane of clear vesicles in the nerve terminal; and (iv) in the matrix of mitochondria. Intracellularly injected Ca accumulates in the mitochondria. Caffeine reduces the electron-dense deposits seen in mitochondria. Caffeine induces a swelling of Golgi apparatus when applied with CaCl2, but this swelling is not observed without CaCl2. These results are discussed in the light of Ca-activated K-conductance increases, which induce 4 types of membrane potential changes [18, 19].

The action of caffeine in promoting ultrastructural damage in frog skeletal muscle fibres. Evidence for the involvement of the calcium-induced release of calcium from the sarcoplasmic reticulum

1. Caffeine at concentrations above 5 mM was shown to cause rapidly extensive ultrastructural damage to the myofibrils of frog skeletal muscle. 2. The effect was promoted at lower temperatures, whereas the myofibrils were protected by prior exposure to procaine. 3. It is argued that caffeine causes a Ca2+-induced release of Ca2+ (the CROC) from the S.R. and that the consequent rise in [Ca2+]i promotes the ultrastructural damage observed. 4. Myofibril digradation is also produced by treatment of the muscle with the divalent cation ionophore A23187; this effect is not protected by either procaine or Dantrolene sodium. 5. It is suggested that A23187 causes the release of Ca2+ from the S.R. by a mechanism that differs from both excitation and the CROC; the resultant rise in [Ca2+]i again causes myofibril degradation. 6. The ways in which a marked rise in [Ca2+]i could cause muscle damage and the possible relevance of these findings to the sequence of events in the development of myopathies of human skeletal muscle are discussed.

Kinetics of functional and morphological changes during decoupling and recoupling induced by glycerol in isolated muscle fibres of the crayfish

The development of ultrastructural changes in the T-system of isolated muscle fibres of the crayfish by the glycerol procedure is described in correlation with the dissociation of excitation-contraction (E--C) coupling as well as with recoupling of the E--C link. The sequence of events in the process of disconnection of the tubules is as follows: dilation of the T-system tubules, disconnection of the constricted tubular segments from the surface membrane and from the T-system vesicle, disappearance of the lumen and its disintegration. The decoupled state is characterised by the presence of round vesicles uniformly distributed in the entire volume of the fibre. The volume of vesicles accounts well for the residual postglycerol volume increase (15%) of the muscle fibres. Functional and structural recovery can be induced by reapplication of glycerol to fibres decoupled and vesiculated with concentrations of glycerol less than or equal to 300mmol.l(-1) in crayfish saline. The restitution starts with the organisation of the material of the disintegrated connecting segment of the T-system tubule into small vesicles which coalesce to form the tubule from the vesicular site. At the same time the surface membrane is invaginated toward the vesicle, thus forming the tubule from the surface membrane site. Recovery starts already in the first minute after application of glycerol and is completed within approximately 15 min.