The behaviour of frog muscle in hypertonic solutions

Abstract

It is well known that hypertonic solutions diminish, and in sufficient concentration abolish, the twitch of frog muscle, whereas hypotonic solutions within a certain range enhance the twitch (Overton, 1902;Fenn, 1936;Hodgkin & Horowicz, 1957). This paper describes some mechanical measurements made with muscles exposed to solutions up to the equivalent of three times the concentration of normal Ringer's solution, and to hypotanic solutions. METHODSAll the experiments described were made with sartorii of English frogs, male and female: no seasonal variations were noticed. Similar results were obtained with the sartorii of toads.Most of the experiments involved measurement of the speed of shortening or of the tension developed. Shortening was recorded by means of a light isotonic lever of low inertia bearing a vane which cast a shadow on a twin phototube (Hill, 1951). The potential change arising from movement of the shadow was amplified by a Kelvin and Hughes amplifier Type 6 and displayed on a smoked drum by a Kelvin and Hughes pen recorder Mk. V. Tension was recorded by means of an R.C.A. 5734 transducer triode and similarly displayed on a smoked drum or, when high amplification and speed were required, photographically from a cathode-ray tube.In early experiments muscles were mounted on a multi-electrode assembly to eliminate the effect of any possible change in the rate of propagation of the contractile wave. This was later found unnecessary and a simple holder bearing two platinum electrodes was adopted, exposing both faces of the muscle to the solution, thus allowing quicker equilibration. Stimulation was direct.The normal Ringer's solution was: (mM) NaCl, 115-5; KCI, 2-5; CaCl, 1-8. Hypotonic solutions were made by adding the calculated amount of distilled water. Hypertonic solutions were of two kinds in which the excess osmotic pressure was provided, (a) by sucrose and (b) by salts. 'Sucrose hypertonic Ringer' was made by dissolving solid sucrose in normal Ringer's solution, assuming 220 mM-sucrose to be isotonic. Salt-enriched solutions were made by dilution of stock solution of 10 x the concentration of standard Ringer's solution in all constituents. Buffering was provided by 2 mM sodium phosphate buffer at pH 7-2. Throughout this paper concentrations are expressed relative to Ringer's solution, e.g. 2-5 x R, or 07 x R. Where the word 'hypotonic' appears it is italicized to make it more easily distinguished from 'hypertonic'.Experiments were made at 00 C and in the region 18-20°C. There was no qualitative difference between results at the two temperatures.

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.…”

Elemental distribution in striated muscle and the effects of hypertonicity: Electron probe analysis of cryo sections

“…The initial release of Ca, presumably from the terminal cisternae, by hypertonic solutions has also been suggested on the basis of the transient contracture (14,51,52,63) and the increase in aequorin signal (94) produced by hypertonicity. Total fiber Ca is not increased, and may be slightly decreased, by hypertonic solutions (14,51), and the increase in the slow component of the exchangeable 45Ca has been interpreted as being due to translocation of Ca into a less readily mobilizable compartment (51).…”

Tension in Skinned Frog Muscle Fibers in Solutions of Varying Ionic Strength and Neutral Salt Composition

“…Since Hodgkin and Horo-wicz (1957) found that in frog muscle fibers normal action potentials could be observed in hypertonic solutions which abolished twitch tension, a number of workers have tried to identify which step beyond activation in the electrochemical coupling process is blocked by the hypertonic solution. Howarth (1958) suggested that the hypertonic solutions, by causing water movement out of the muscle, concentrated the internal salts and directly affected the interaction of the contractile material, causing a decreased contractile tension. Support for this hypothesis was provided by the studies of April et al (1968) and by us .…”