Abstract
The effects of substrate condition and ADPβS on the pCa 2+-tension relationships were investigated, using α-toxin permeabilized rabbit mesenteric artery at 37°C. The contraction induced by 10 μM Ca 2+ solution after permeabilization was as large as that induced by 145 mM K + PSS solution containing 10 μM NE in the intact tissue, indicating that the majority of the cells were permeabilized. The Ca 2+ sensitivity was greatly affected by the substrate condition and increasing the ratio of ATP CP induced a leftward shift of the pCa 2+-tension curve. Addition of 100 μM ADPβS had a similar effect. When the ATP CP ratio was high, the 0.1 μM Ca 2+ solution relaxed the tissue precontracted by 10 μM Ca 2+ solution more slowly showing hysteresis. One mM vanadate, which is reported to relax muscle by forming actomyosin-ADP-Vi (AM-ADP-Vi), completely inhibited both contractions induced by 0.18 μM Ca 2+ solution containing 2 mM MgADP and 0.3 μM Ca 2+ solution containing 0.3 μM PDBu. These results indicated that the population of AM-ADP complex in the crossbridge had increased due to the accumulation of ADP inside the tissue or activation of PKC and that the inhibition of ADP release from AM-ADP complex may be playing a key role in increasing Ca 2+ sensitivity of myofilaments.
Published Version
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