Approximating the isometric force-calcium relation of intact frog muscle using skinned fibers

In previous papers we used estimates of the composition of frog muscle and calculations involving the likely fixed charge density in myofibrils to propose bathing solutions for skinned fibers, which best mimic the normal intracellular milieu of intact muscle fibers. We tested predictions of this cal...

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Bibliographic Details
Published in:	Biophysical journal Vol. 69; no. 4; pp. 1484 - 1490
Main Authors:	Maughan, D.W., Molloy, J.E., Brotto, M.A., Godt, R.E.
Format:	Journal Article
Language:	English
Published:	United States Elsevier Inc 01-10-1995
Subjects:	Adenosine Triphosphatases - metabolism Adenosine Triphosphate - metabolism Animals Calcium - pharmacology In Vitro Techniques Isometric Contraction - drug effects Membrane Potentials Models, Biological Muscle Fibers, Skeletal - drug effects Muscle Fibers, Skeletal - physiology Muscle, Skeletal - physiology Myofibrils - drug effects Myofibrils - physiology Predictive Value of Tests Rana temporaria Reproducibility of Results Temperature Vanadates - pharmacology
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Summary:	In previous papers we used estimates of the composition of frog muscle and calculations involving the likely fixed charge density in myofibrils to propose bathing solutions for skinned fibers, which best mimic the normal intracellular milieu of intact muscle fibers. We tested predictions of this calculation using measurements of the potential across the boundary of skinned frog muscle fibers bathed in this solution. The average potential was -3.1 mV, close to that predicted from a simple Donnan equilibrium. The contribution of ATP hydrolysis to a diffusion potential was probably small because addition of 1 mM vanadate to the solution decreased the fiber actomyosin ATPase rate (measured by high-performance liquid chromatography) by at least 73% but had little effect on the measured potential. Using these solutions, we obtained force-pCa curves from mechanically skinned fibers at three different temperatures, allowing the solution pH to change with temperature in the same fashion as the intracellular pH of intact fibers varies with temperature. The bath concentration of Ca2+ required for half-maximal activation of isometric force was 1.45 microM (22 degrees C, pH 7.18), 2.58 microM (16 degrees C, pH 7.25), and 3.36 microM (5 degrees C, pH 7.59). The [Ca2+] at the threshold of activation at 16 degrees C was approximately 1 microM, in good agreement with estimates of threshold [Ca2+] in intact frog muscle fibers.
Bibliography:	ObjectType-Article-1 SourceType-Scholarly Journals-1 ObjectType-Feature-2 content type line 23
ISSN:	0006-3495 1542-0086
DOI:	10.1016/S0006-3495(95)80019-6