Rapid relaxation of single frog skeletal muscle fibres following laser flash photolysis of the caged calcium chelator, diazo‐2

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Abstract
Diazo-2 is a calcium chelator based on BAPTA [(1989) J. Biol. Chem., in press], whose electron withdrawing diazoacetyl group may be rapidly (2000 s−1) converted photochemically to an electron donating carboxymethyl group by exposure to near ultraviolet light, producing an increase in its calcium affinity (K d changes from 2.2μM to 0.073 μM) without steric modification of the metal binding site. Photolysis of a 2 mM solution of this compound with a brief flash of light from a frequency-doubled ruby laser (347 nm) caused single skinned muscle fibres from the semitendinosus muscle of the frog Rana temporaria to relax with a mean half-time of 60.4±5 ms (range 30–100 ms, n = 15) at 12°C, which is faster than the relaxation observed in intact muscles (half-time 133 ms at 14°C [(1986) J. Mol. Biol. 188, 325–342]) and similar to the rate of the fast phase of tension decay in intact single fibres (20 s−1 at 1O°C [(1982) J. Physiol. 329, 1–20]).