Ca-EGTA affects the relationship between [Ca2+] and tension in α-toxin permeabilized rat anococcygeus smooth muscle
✍ Scribed by Godfrey L. Smith; Catherine A. Crichton
- Publisher
- Springer Netherlands
- Year
- 1993
- Tongue
- English
- Weight
- 805 KB
- Volume
- 14
- Category
- Article
- ISSN
- 0142-4319
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✦ Synopsis
The relationship between calcium concentration ([CaZ+]) and force in smooth muscle can be studied by perrneabilizing the sarcolemma and bathing the preparation in a mock intracellular solution. Normally [Ca'+] is set in these solutions using the Ca2+ chelator EGTA in the concentration range of 4-10 mM. This study shows that lowering total EGTA concentration ([EGTA],) below 10 mM depresses Ca2+ -activated force generated in 0.1 pM Ca'+. The observed threshold for the effect of EGTA, is 0.2 mM, and the effect is maximal at approximately 10 mM. BAPTA, another Ca" chelator, also produces this effect. Tension production in smooth muscle is controlled by actomyosin interaction. This in turn is mediated by the relative activities of myosin light chain kinase (MLCK) and phosphatase (MLCP). Inhibiting MLCP with Microcystin LR (10 PM), an increase [EGTA,] from 0.2 mM to 10 mM still enhanced force. This suggests that EGTA promotes phosphorylation of myosin by the activation of MLCK and not by inhibition of MLCP.