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Thapsigargin does not affect phenylephrine-induced contractions in the anococcygeus muscle of rats
1Laboratory of Pharmacology, College of Pharmaceutical Sciences, University of Sao Paulo, Ribeirao Preto, Brazil.
Insights
Intracellular calcium significantly contributes to phenylephrine-stimulated contractions in rat anococcygeus smooth muscle. However, the calcium store activated by phenylephrine is not sensitive to thapsigargin.
Area of Science:
- Pharmacology
- Physiology
- Smooth Muscle Biology
Background:
- Intracellular calcium stores play a critical role in smooth muscle contraction.
- Understanding the specific calcium pathways involved in phenylephrine-induced contractions is essential for elucidating smooth muscle function.
Purpose of the Study:
- To investigate the role of intracellular calcium in phenylephrine-stimulated contractions of rat anococcygeus smooth muscle.
- To evaluate the effects of thapsigargin and TMB-8, antagonists of intracellular calcium stores, on these contractions.
Main Methods:
- Functional studies were employed to assess smooth muscle contractions.
- Phenylephrine-induced contractions were measured in calcium-free media.
- The effects of thapsigargin and 8-(Diethylamino)-octyl-3,4,5-trimethoxybenzoate, HC1 (TMB-8) were evaluated.
Main Results:
- Phenylephrine induced concentration-related contractions in calcium-free media, persisting for approximately 26 stimulations.
- TMB-8 (10 microM) rightward shifted phenylephrine concentration-response curves, reducing maximum contraction by 39.2% without altering EC50.
- Thapsigargin (1 microM) did not affect phenylephrine-stimulated contractions in calcium-free media.
Conclusions:
- Intracellular calcium is crucial for phenylephrine-stimulated contractions in rat anococcygeus smooth muscle.
- The phenylephrine-sensitive intracellular calcium store is not sensitive to thapsigargin, suggesting a distinct calcium release mechanism.
Abstract:
1. The aims of the present study were to investigate the contribution of intracellular calcium and to evaluate the effect of the antagonists of the intracellular calcium stores, thapsigargin and [8-(Diethylamino)-octyl-3,4,5-trimethoxybenzoate, HC1] TMB-8, on phenylephrine-stimulated contractions of rat anococcygeus smooth muscle, using functional studies. 2. Phenylephrine induced concentration-related contractions in both 2.5 mM Ca2(+)-free EGTA media. 3. In Ca2(+)-free media phenylephrine stimulated successive contractions, and the contractile response was abolished only after approximately 26 stimulations. 4. In Ca2(+)-free media, after incubation with 10 microM TMB-8 for 30 min, phenylephrine induced concentration-response curves that shifted to the right. The EC50 values were not changed, and the maximum contractile response was reduced by 39.2 +/- 7.6% in relation to phenylephrine-stimulated responses in absence of TMB-8. 5. Thapsigargin (1 microM) did not alter phenylephrine-stimulated contractions in Ca2(+)-free media. 6. These results indicate that intracellular Ca2+ plays an important role on phenylephrine-stimulated contractions on rat anococcygeus muscle and that the phenylephrine-sensitive intracellular Ca2+ store is not sensitive to thapsigargin.