Dynamics of smooth muscle contraction

Photolysis of caged calcium (Nitr5, Calbiochem®) can be used to studycalcium dependent processes such as excitation-contraction coupling andmuscular mechanics. Expensive high energy light sources are routinely used forUV light exposure; this study describes an alternative low cost Xenon flash unitconstmcted in our laboratOlY. A 300 J short arc Xenon flash lamp (Heimarl1l®)was mounted in an elliptical reflector and driven by a modified Metz® 60 CT 4photo flash unit up to 240 J input energy and 4 ms flash duration. A 20 I cuvettecontaining a test solution was placed in a complementmy elliptical reflector. Anion selective calcium electrode was used to measure the free calciumconcentration [CaH] before and after flash in test solutions containing 1.00 mMNitr5 in combination with different added [CaH]'s. Using this technique weestimated that I flash on 1.00 mM Nitr5 increased the free [CaH] from 10. to1.1*10" M. When the added [CaH] was less than 2.3*10'" M, the used Nitr5behaved as a strong calcium chelator because 23% of it was unloaded withcalcium. It is concluded that a physiologically relevant change in free [CaH] canbe evoked by photolysis ofNitr5 using a low cost (approximately $1500) Xenonflash unit, and that ion selective Ca electrodes can be adequately used to monitorthe resulting changes in [CaH].