Frog muscle

Time-resolved x-ray diffraction of frog muscle confirmed movement of the cross-bridges... 

Nassar-Gentina, V., Passonneau, J.V., Rapoport, S.I. (1981). Fatigue and metabolism of frog muscle fibers during stimulation and in response to caffeine. Am. J. Physiol. 241, CI60-C166. 

Using the cell-attached patch clamp technique on frog muscle fibers (79), one can observe only two conditions the open, conducting state of the receptor and a nonconducting state of unknown identity. The transitions behave according to stochastic principles the lifetimes of any particular condition are distributed exponentially. The open state has a mean duration that is the inverse of the rate of channel closing. Because channel open time depends only upon a conformational shift, agonist concentration does not influence the parameter. It is, however, influenced... 

Figure 3. (+)-Anatoxin-a (AnTx) and ACh induced single ion channel currents in isolated frog muscle fibers. Open channels with 32 pS conductance are downward deflections (inward current at hyperpolarized potentials). The currents shown on the left are all at one potential. The duration of channel open events had a similar voltage-dependence for both ACh and (+)-anatoxin-a. With ACh, the events were most often singular, while with (+)-anatoxin-a the events were shorter and were more frequently paired so that the mean duration of the exponentially distributed open times and selected membrane holding potentials was approximately one-half, independent of the concentration of the agonist applied.

An outer cell membrane separates the intracellular solution or cytoplasm from the extracellular solution. These two solutions differ in their compositions. The extracellular fluid contains primarily Na and CH ions (0.1 to 0.5 M) as well as minor amounts of K+, Ca, and Mg ions, while the cytoplasm has a high concentration of K+ ions (0.1 to 0.5M) and low concentrations of Na and CH ions. Principal anions in the cytoplasm are the relatively large anions of different organic acids, incfuding pofyanions. As an example we report the major inorganic ions contained in the extra- and intracellular solutions of frog muscle (inniM) ... 

In the cell s nonexcited state (see Section 30.1.3), the membrane potential, (p , is always negative (i.e., the cytoplasm is negatively charged relative to the extracellular solution). For different cell types the values of (p vary between -50 and -100 mV for frog muscle the value is -90 mV. 

It had been known from at least the time of Pasteur that the presence of sodium or potassium phosphate aided the progress of a yeast fermentation. Later intensive study showed that a complex group of enzymes (phosphatases and phosphorylases) was responsible for the phosphorylation, dephosphorylation and interconversion of D-glucose 6-phosphate, D-fructose 6-phosphate, D-fructose 1,6-diphosphate and similar substances in various types of cells and muscle tissue. Detailed reviews of the field are available. - A further advance was made in 1936, when Cori and Cori noted that in certain circumstances well-washed frog muscle immersed in a sodium phosphate buffer utilized the inorganic phosphate to produce a new hexose phosphate (the Cori ester). This compound was later shown to be a-D-glucopyranose-l-phosphate and yielded crystalline dipotassium and brucine salts. The Cori ester arose because... 

Keynes RS, Swan RC The permeability of frog muscle fibers to hthium ions. J Physiol 147 626-638, 1959... 

Galvani, Luigi (1737—1798). An Italian physician and anatomist who discovered the galvanic current in the course of working with frog muscles... 

Reproduced, with permission, from Marshall CG, Ogden DC, Colquhoun D The actions of suxamethonium (succinyldicholine) as an agonist and channel blocker at the nicotinic receptor of frog muscle. J Physiol [Lond] 1990 428 155.)... 

Fig. 12. The generated power density vs load for various gel films made under different conditions. The power density of frog muscle is indicated for comparison...

AMP aminohydrolase, an enzyme relatively specific for AMP, has been observed in reptiles (44), erythrocytes (38), snail (45), unfertilized fish eggs (46), invertebrates (47), a variety of mammalian tissues (20), and a particulate fraction of pea seeds (48). Evidence suggests that the frog muscle AMP aminohydrolase is located within or just beneath the sarcolemma (49). The rabbit skeletal and heart muscle enzymes were found in the cytoplasm and mitochondria (20, Jfi, 50, 51), while the enzyme of kidneys and gills of freshwater fish was located in the cytoplasmic fraction (52). The enzyme occurs in most areas of the rat (53) and rabbit brain (54). The nonspecific enzyme from several microbial sources deaminates adenosine triphosphate (ATP) and adenosine diphosphate (ADP) as well as AMP (see Section V). 

Tanner [49] measured diffusion coefficients of water in three different types of frog muscle cells. He used a variety of magnetic field gradient techniques so as to cover a wide range of diffusion times A= 1 ms to 1 s. The time dependence of the diffusion coefficient was analyzed to obtain the intracellular diffusion coefficients and estimates of the permeability of the cell membranes. In restricted diffusion studies three 90 degree r.f. pulse sequences (stimulated echo) are often used which provides PG-NMR experiments with long diffusion times to explore the dependence of diffusion time on the echo attenuation [49]. 

Ling and Negendank have determined the water uptake of frog muscle from humid air (Fig. 35)255. After taking up 3—5% of the total amount, a co-operative adsorption of water is observed like a capillar or multilayer-condensation. 

Fig. 35. Uptake of water by frog muscle at various relative water vapour pressure (Ling and Negendank255 )...

Bagni, M. A., Cecchi, G., and Colombini, B. (2002). A non-cross-bridge stiffness in activated frog muscle fibers. Biophys.J. 82, 3118-3127. 

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