Influence of osmotic strength on cross‐section and volume of isolated single muscle fibres

Abstract

Despite long-continued interest in the subject, uncertainty still exists about some fundamental aspects of the osmotic behaviour of striated muscle cells. One unsettled problem has to do with the extent to which the fibre adjusts its volume in response to changes in the osmotic pressure of the bathing medium. There is abundant evidence, both from indirect observations and from direct measurements of volume, that under conditions in which one might expect the transfer of solutes across the cell membrane to be slight and over a moderate range of osmotic strengths, the striated muscle fibre exhibits ideal or nearly ideal osmotic behaviour (in the sense that it behaves as a freely distensible semipermeable bag containing a fixed amount of solute and a certain amount of solid or osmotically inactive matter) (e.g. Sato, 1954a; Dydynska & Wilkie, 1963;Reuben, Lopez, Brandt & Grundfest, 1963). However, recent studies in which changes in fibre volume were estimated from measurements of the widths of single muscle fibres have suggested departures from ideal behaviour at very high and very low osmotic strengths. Dydynska & Wilkie (1963) found that the widths of fibres in the sternocutaneus muscle of the frog did not decrease as much as would have been expected when the muscle was placed in solutions whose osmotic strength had been made more than twice normal by the addition of sucrose. This finding was in contrast with the results of their chemical estimates of fibre water in the sartorius muscle, which indicated that the muscle fibres exhibited ideal osmotic behaviour up to osmotic strengths at least four times that of the normal bathing solution. Reuben et al. (1963) estimated changes in the volume of isolated single fibres of the semitendinosus muscle of the frog, and found that the fibres appeared to swell less than might have been expected when the osmotic strength of the bathing solution was reduced by more than half. This finding is in qualitative agreement with the results of some chemical estimates of fibre water made on whole muscles by Grieve

Ca2+ Influx via the Na+/Ca2+ Exchanger Is Enhanced in Malignant Hyperthermia Skeletal Muscle

“…Here we show that detubulation of MHN and MHS swine fibers induces a small increase in [Ca 2ϩ ] r in both types of muscle fibers (16% MHN and 10% MHS, respectively). This increment may be related to the change in muscle volume, water moving out the cell, upon exposure to hypertonic solution, because striated muscle behaves as a perfect osmometer, decreasing its volume in proportion to the tonicity of the bathing medium (53,54). The increase in [Ca 2ϩ ] r provoked by Na ϩ -free solution after muscle detubulation is reduced by 62% in MHN and 68% in MHS compared in non-detubulated muscle fibers.…”

Intramembrane charge movements in frog skeletal muscle in strongly hypertonic solutions.

“…These include administrations of tetracaine, dantrolene Na, Ca 2+ deprivation, and nifedipine (Putney and Bianchi, 1974;Huang, 1981aHuang, , 1990Huang, , 1991Hui, 1983;Bruin, Fitts, Pizarro, and Rios, 1988;Rios and Brum, 1987). The physiological effects of changes in extracellular tonicity have been attributed to changes in intracellular ionic strength arising from the consequent fiber volume change (Howarth, 1958;Dydynska and Wilkie, 1963;Blinks, 1965;Caputo, 1968;Gordon and Godt, 1970). The mechanism for their influence on charge may therefore differ from those of the pharmacological agents.…”

The effect of diameter on the electrical constants of frog skeletal muscle fibres

“…One source of error arose from the fact that muscle fibres are rarely circular in cross-section. Blinks (1965) compared the average value of actual cross-sectional area with the estimated areas based on (1) the circular, or (2) elliptical assumption (Gordon, Huxley & Julian, 1966). His result showed that on the circular assumption the estimated area was 121 %, and on the elliptical assumption 104 % of the actual area.…”

“…2A, B). pressure (Dydynska & Wilkie, 1963;Reuben, Lopez, Brandt & Grundfest, 1963;Blinks, 1965), G, ought to increase with osmotic pressure. An increase of myoplasmic viscosity might be responsible for this unexpected reduction of Gi.…”