The effects of changes in temperature or ionic strength on isolated rabbit and fish skeletal muscle thick filaments

Abstract

Although the skeletal muscles of different vertebrate species have been assumed to be generally similar, recent X-ray diffraction and mechanical studies have demonstrated differences in the responses of these muscles to changes in physiological conditions. X-ray diffraction studies have indicated that lowering the temperature and lowering ionic strength may affect the crossbridge arrangement of rabbit thick filaments. Similar X-ray diffraction studies on the structural effects of lowering ionic strength in frog and fish muscles are less clear in interpretation, while lowering the temperature appears to have little effect in these muscles. In the present study we have compared the effects of lowering the temperature or ionic strength on the crossbridge order of isolated rabbit and fish thick filaments as observed in the electron microscope. In agreement with the X-ray results, rabbit filaments show a distinct loss of crossbridge order when stained at 4 degrees C compared to 25 degrees C, whereas fish thick filaments appear similar at both temperatures. Rabbit thick filaments, when diluted to one-fourth of the normal ionic strength (while maintaining constant EGTA and ATP concentration), showed a strong tendency to bind to actin filaments, while similarly-treated fish filaments showed little tendency to aggregate or become disordered. These results appear to support the X-ray diffraction results of other investigators, and the idea that effects of ionic strength or temperature on muscle may vary with species.

The chicken muscle thick filament: temperature and the relaxed cross-bridge arrangement

“…In warm-blooded animals, this adaptation to varying temperature is not usually a consideration, since these muscles do not normally operate physiologically at a temperature which would cause disordering. These results support our earlier conclusion (Kensler et al, 1994) that temperature is an important parameter which must be taken into account during studies of vertebrate skeletal muscle. Our results may also explain the relative paucity of previous studies on the structural arrangement of myosin in the chicken thick filament.…”

“…Both of these animals lose their cross-bridge order if the temperature of the muscle or filaments is lowered to low temperatures. In contrast, we have shown that in fish, a cold-blooded animal in which body temperature is not rigorously controlled, a similar lowering of temperature does not appear to cause a large loss of cross-bridge order (Kensler et al, 1994). This difference between warm-blooded and cold-blooded animals may relate to the physiological parameters under which the muscles operate, and the importance of the ordered relaxed cross-bridge arrangement.…”

“…1B), than in the filaments stained at 25 ° C (Fig. 1A), thus suggesting that the chicken filaments are sensitive to temperature, as previously reported for rabbit filaments 0Nray, 1987; Wakabayshi et al, 1988;Schr6der et al, 1990;Kensler et al, 1994). For this reason, only chicken filaments negatively stained at 25°C were used for further structural analysis.…”

“…The recent demonstration by Wray (1987) and Wakabayashi and colleagues (1988) by X-ray diffraction that rabbit filaments are temperature sensitive and lose their relaxed cross-bridge order at lower temperatures, suggested the possibility that chicken thick filaments might also be temperature sensitive. To examine this, we compared the appearance of the isolated chicken filaments negatively stained at either 25 ° C or in the cold room (4 ° C), as in our previous studies of rabbit thick filaments (Kensler et al, 1994). Figure 1A shows a field of isolated chicken thick filaments in which the negative staining was carried out with all the solutions at 25 ° C. Many of these filaments (asterisks) show a periodic appearance similar to that previously shown for frog (Kensler & Stewart, 1983, fish (Kensler & Stewart, 1989), and rabbit (Kensler & Stewart, 1993).…”

“…in this respect to rabbit muscle thick filaments, which have been shown by X-ray diffraction (Wray, 1987;Wakabayshi et al, 1988;Lowy et al, 1991) and electron microscopy (Schr6dinger et al, 1990;Kensler et al, 1994) to lose their relaxed helical arrangement of the cross-bridges at low temperatures. Wray (1987) has presented evidence in the case of the rabbit that this loss of cross-bridge order may be due to differences in the state of hydrolysis of the nucleotide bound to the myosin head.…”