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Diazepam effects on frog skin cyclic nucleotide phosphodiesterase
M Margiotta1, P G Borasio, C Ardizzone
1Institute of General Physiology, University of Bari, Italy.
General Pharmacology
|January 1, 1989
Summary
Skin homogenates of Rana esculenta contain two cyclic adenosine monophosphate phosphodiesterases (cAMP-PDEs). Diazepam inhibits both low and high Km cAMP-PDE enzymes competitively.
Area of Science:
- Biochemistry
- Pharmacology
- Zoology
Background:
- Cyclic adenosine monophosphate phosphodiesterases (cAMP-PDEs) regulate intracellular cyclic adenosine monophosphate (cAMP) levels.
- Understanding cAMP-PDE activity in amphibian skin is crucial for studying physiological responses.
Purpose of the Study:
- To characterize the kinetic properties of cAMP-PDEs in Rana esculenta skin.
- To investigate the effect of calcium on cAMP-PDE activity.
- To determine the inhibitory effect of diazepam on cAMP-PDEs.
Main Methods:
- Enzyme kinetic assays were performed on skin homogenates of Rana esculenta.
- Determination of Michaelis-Menten constants (Km) and maximal velocities (Vmax).
- Assessment of enzyme activity in the presence of varying calcium concentrations and diazepam concentrations.
Main Results:
- Two distinct cAMP-PDE enzymes were identified: a low Km PDE (Km = 0.42 x 10(-6) M) and a high Km PDE (Km = 180 x 10(-6) M).
- Only the high Km PDE activity was stimulated by calcium.
- Diazepam (1-0.5 mM) competitively inhibited both low and high Km cAMP-PDE enzymes.
Conclusions:
- Rana esculenta skin possesses at least two cAMP-PDE isoenzymes with different kinetic properties.
- Calcium specifically modulates the high Km cAMP-PDE.
- Diazepam exhibits competitive inhibition against both cAMP-PDE isoenzymes in this tissue.