Rapid activation by photolysis of nitr-5 in skinned fibres of the striated adductor muscle from the scallop

Trevor J. Lea, Mark J. Fenton, James D. Potter, Christopher C. Ashley

Research output: Contribution to journalArticlepeer-review

9 Scopus citations


Photolysis of nitr-5, a caged calcium molecule, has been used for rapid activation of skinned fibre bundles of a myosin-regulated muscle, the striated adductor of the scallop, Pecten maximus. Chemically skinned fibre bundles (diameter 70-200 μm) were equilibrated in solutions containing 1-3 mM nitr-5 (pCa 6.1) and then activated by ultraviolet laser pulse (25 ns). Pulse energies of 60-95 mJ gave contractions of over 90% maximum tension and a mean half-time for tension rise of 43 ms (n = 4) at 12°C. Electrically stimulated bundles of intact fibres develop a tetanus with a rise half-time of 60.2 ms at 10°C (n = 5) (Rall, J.A. (1981) J. Physiol. 321, 287-295, and personal communication). At lower pulse energies the skinned fibres gave smaller amplitude contractions with slower rates of rise (up to 260 ms half-time). In addition, a slower component of tension development (mean rise half-time 13.3 s) was often observed. In ATP-free solutions containing hexokinase and glucose, rigour tension developed with a delayed onset. Rapid release of ATP (0.47-0.59 mM) from photolysis of caged ATP (2 mM) at pCa 4.5 then caused a rapid contraction with a mean half-time for tension development of 17 ms (n = 4). The fast activation rates obtained by the photorelease of Ca2+ from nitr-5 are similar to those obtained with skinned skeletal fibres of actin-regulated muscle. The results imply that the rate-limiting step in excitation-contraction coupling of the scallop muscle is not the increase in sarcoplasmic Ca2+, but rather the activation of the muscle in response to this increase. The half-times of ATP-induced contractions at pCa 4.5 suggest that in a contraction activated by a rapid Ca2+ jump the process comprising ATP hydrolysis and cross-bridge cycling occurs at a somewhat faster rate than the Ca2+-dependent activation process which preceds it.

Original languageEnglish (US)
Pages (from-to)186-194
Number of pages9
JournalBBA - General Subjects
Issue number2
StatePublished - May 16 1990


  • (Scallop muscle)
  • Caged calcium
  • Calcium ion
  • Laser photolysis
  • Muscle contraction
  • Skinned muscle fibre

ASJC Scopus subject areas

  • Biochemistry
  • Biophysics
  • Molecular Biology


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