Measurement of intracellular Ca2+ concentration changes by use of fura-2 in the generation of myogenic contraction of dog cerebral artery in response to quick stretch.

In the present study, by using fura-2, we attempted to measure the changes of intracellular free Ca2+ concentrations ([Ca2+]i) in the generation of myogenic contraction of dog cerebral artery in response to quick stretch. Quick stretch was applied to rubber sheets or dog cerebral arteries at a rate of 10 cm/sec for 30 sec with the amount of stretch equivalent to 40% of the initial length of materials. In rubber sheets and fura-2-unloaded cerebral arteries, the intensities of 500 nm fluorescence due to excitation at 340 nm (F340) and 380 nm (F380) were reduced by quick stretch although the ratio signal (F340/F380:R340/380) was not appreciably affected. F340, F380, and R340/380 remained unchanged for 30 sec of the stretch period. By contrast, in fura-2-loaded cerebral artery segments, before the appearance of delayed contraction in response to quick stretch, R340/380 was enormously raised by the mechanical stimulation. The stretch-induced myogenic contraction and the corresponding change in R340/380 were abolished by repeated stretches of the artery segments in Ca(2+)-free medium containing 0.2 mM EGTA or in the presence of papaverine (10(-4) M). L-type Ca2+ channel antagonists (nicardipine and d-cis-diltiazem) inhibited both [Ca2+]i and mechanical activity of the cerebral arteries in response to stretch in a concentration-dependent and parallel manner. These findings indicate that changes of R340/380 in the generation of myogenic contraction of fura-2-loaded dog cerebral artery in response to quick stretch reflect those of [Ca2+]i in the response. Fura-2 seems to be a useful Ca2+ indicator to measure the Ca2+ mobilization of vascular smooth muscle in response to quick stretch at the whole tissue level.