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First published online January 31, 2006
Journal of Experimental Biology 209, 668-676 (2006)
Published by The Company of Biologists 2006
doi: 10.1242/jeb.02033
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Effect of pH on the rate of myosin head detachment in molluscan catch muscle: are myosin heads involved in the catch state?

Marion Christine Höpflinger, Olena Andruchova, Oleg Andruchov, Herbert Grassberger and Stefan Galler*

Department of Cell Biology, University of Salzburg, Hellbrunnerstr. 34, A-5020 Salzburg, Austria


Figure 1
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  		Fig. 1. (A) Force recording of a skinned fibre bundle of anterior byssus retractor muscle (ABRM) of common muscle Mytilus edulis. The spikes represent the force responses following repetitive stretches (0.2 Hz, 0.2% of the fibre length in amplitude and 0.2 s in duration), which serve as a measure of stiffness. The solution sequence is indicated. (B) Force-stiffness diagram of another ABRM fibre bundle undergoing the protocol shown in A. The stiffness (mN/%L0) was calculated by relating the maximal positive amplitude of the stretch-induced force peaks (mN) to the (constant) relative length change (%L0). Open circles, activation solution at pH 6.7; open triangles, relaxation solution at pH 6.7; filled triangles, relaxation solution at pH 7.4.

 

Figure 2
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  		Fig. 2. Original force recordings of stretch experiments on maximally Ca2+-activated (pCa 4.5) skinned anterior byssus retractor muscle (ABRM) fibre bundles. (A-C) High time resolution force recordings during stretch experiments under indicated conditions. Control (pH 6.7) and test recordings of each set were obtained on the same fibre bundle and at the same stretch amplitude. Note that the delayed force increase (time parameter t3) and the immediate force decay following stretch (time parameter t2) are slowed by moderate alkalisation.

 

Figure 3
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  		Fig. 3. ATP step experiments starting at high force rigor. A stepwise increase of ATP concentration was induced by flash photolysis of caged ATP. (A) Force recording at low time resolution, indicating the conditions for induction of high-force rigor and subsequent force decay induced by an ATP step. (B) Superimposed force recordings at high time resolution of ATP step under control (pH 6.7) and test conditions (pH 7.4).

 

Figure 4
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  		Fig. 4. Superimposed force recordings of ATP step experiments starting at low force rigor at pH 6.7 and pH 7.4. The force was normalised to that measured 10 s after flash. The force increase was induced by a stepwise increase of ATP concentration after induction of low-force rigor in the presence of high Ca2+ concentration (pCa 4.5).

 




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