Intracellular @entity141 was determined with the @entity593 technique during electrically induced contractions in the @entity95 rectococcygeus smooth muscle at 22 degreesC. The muscles were electrically activated to give short, reproducible contractions. Intracellular [ @entity141 ] increased during activation; the increase in [ @entity141 ] preceded force development by approximately 2 s. After cessation of stimulation @entity141 fell, preceding the fall in force by approximately 4 s. The fluorescence properties of @entity593 were determined with time-resolved spectroscopy using synchrotron light at the MAX-storage ring, Lund, Sweden. The fluorescence decay of free @entity593 was best described by two exponential decays (time constants approximately 0.5 and 1.5 ns) at low @entity141 (pCa 9). At high @entity141 (pCa 4.5), fluorescence decay became slower and could be fitted by one exponential decay (1.9 ns). Time-resolved anisotropy of free @entity593 was characteristic of free rotational motion (correlation time 0.3 ns). Motion of @entity593 could be markedly inhibited by high concentrations of @entity908 kinase. Time-resolved spectroscopy measurements of muscle fibers loaded with @entity593 showed that the fluorescence lifetime of the probe was longer, suggesting an influence of the chemical environment. Anisotropy measurements revealed, however, that the probe was mobile in the cells. The @entity141 -dependence of contraction and relaxation was studied using a photolabile @entity460 chelator, @entity54670 , which could be loaded into the muscle cells in a similar manner as @entity593 . Photolysis of @entity54670 leads to an increase in its @entity141 -affinity and a fall in free @entity141 . When muscles that had been loaded with @entity54670 were illuminated with UV light flashes during the rising phase of contraction, the rate of contraction became slower, suggesting a close relation between intracellular @entity141 and the cross-bridge interaction. In contrast, photolysis during relaxation did not influence the rate of force decay, suggesting that relaxation of these contractions is not determined by the rate of @entity141 removal or due to an increased @entity141 sensitivity, but instead is limited by other processes such as deactivation by dephosphorylation or detachment of tension-bearing cross-bridges, possibly regulated by thin filament systems.

@entity460 transients and the effect of a photolytically released XXXX chelator during electrically induced contractions in @entity95 rectococcygeus smooth muscle.

@entity908 :: ('MESH:D003401', 'Chemical') :: ['creatine'] @entity95 :: ('9986', 'Species') :: ['rabbit'] @entity54670 :: ('MESH:C063685', 'Chemical') :: ['diazo-2'] @entity593 :: ('MESH:D016257', 'Chemical') :: ['fura-2'] @entity460 :: ('MESH:D002118', 'Chemical') :: ['calcium'] @entity141 :: ('CHEBI:29108', 'Chemical') :: ['Ca2+']
@entity460 :: (MESH:D002118,Chemical) :: ['calcium']
