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Ontogenic expression of acetylcholinesterase activity in trachealis of young swine

Publication ,  Journal Article
Murphy, TM; Mitchell, RW; Phillips, IJ; Leff, AR
Published in: American Journal of Physiology - Lung Cellular and Molecular Physiology
1991

Previous investigations have demonstrated that cholinergic contraction of porcine tracheal smooth muscle (TSM) decreases between the second and tenth weeks of life. In this investigation, we hypothesized that the greater contractile response to acetylcholine (ACh) in TSM of 2-wk-old swine (2ws) vs. 10-wk-old swine (10ws) was the result of a relative decrease in activity of acetylcholinesterase (AChase). To examine this hypothesis, we assessed AChase activity directly in homogenates of TSM from eight 2ws and seven 10ws using a newly adapted method that measures the rate of cleavage of acetylthiocholine; enzyme activity was expressed as absorbance units per minute per milligram protein. The AChase from tissues of both age groups saturated at ~3 mM substrate. However, maximal AChase activity (V(max)) was significantly greater in 10ws than 2ws. Eadie-Hofstee analysis of enzyme kinetics revealed similar Michaelis-Menten constants for 2ws and 10ws. The concentration of physostigmine (PS), an inhibitor of cholinesterase, that elicited half-maximal inhibition of AChase activity also was similar for 2ws and 10ws. In separate studies, contraction of TSM strips was assessed in vitro at optimal resting length and expressed as a function of maximal force generation to potassium chloride. Strips of TSM from 2ws contracted with greater force than those of 10ws. After pretreatment with 10-8 M PS, contractile forces were similar in 2ws and 10ws. We conclude that AChase activity measured directly in muscle homogenates is significantly reduced in TSM of 2ws vs. 10ws and that this may result in augmented contraction to ACh under conditions of zero-order kinetics.

Duke Scholars

Published In

American Journal of Physiology - Lung Cellular and Molecular Physiology

Publication Date

1991

Volume

261

Issue

4 5-2

Start / End Page

L322 / L326

Related Subject Headings

  • Respiratory System
  • 1116 Medical Physiology
  • 0606 Physiology
 

Citation

APA
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ICMJE
MLA
NLM
Murphy, T. M., Mitchell, R. W., Phillips, I. J., & Leff, A. R. (1991). Ontogenic expression of acetylcholinesterase activity in trachealis of young swine. American Journal of Physiology - Lung Cellular and Molecular Physiology, 261(4 5-2), L322–L326.
Murphy, T. M., R. W. Mitchell, I. J. Phillips, and A. R. Leff. “Ontogenic expression of acetylcholinesterase activity in trachealis of young swine.” American Journal of Physiology - Lung Cellular and Molecular Physiology 261, no. 4 5-2 (1991): L322–26.
Murphy TM, Mitchell RW, Phillips IJ, Leff AR. Ontogenic expression of acetylcholinesterase activity in trachealis of young swine. American Journal of Physiology - Lung Cellular and Molecular Physiology. 1991;261(4 5-2):L322–6.
Murphy, T. M., et al. “Ontogenic expression of acetylcholinesterase activity in trachealis of young swine.” American Journal of Physiology - Lung Cellular and Molecular Physiology, vol. 261, no. 4 5-2, 1991, pp. L322–26.
Murphy TM, Mitchell RW, Phillips IJ, Leff AR. Ontogenic expression of acetylcholinesterase activity in trachealis of young swine. American Journal of Physiology - Lung Cellular and Molecular Physiology. 1991;261(4 5–2):L322–L326.

Published In

American Journal of Physiology - Lung Cellular and Molecular Physiology

Publication Date

1991

Volume

261

Issue

4 5-2

Start / End Page

L322 / L326

Related Subject Headings

  • Respiratory System
  • 1116 Medical Physiology
  • 0606 Physiology