Ca-EGTA affects the relationship between [Ca2+] and tension in alpha-toxin permeabilized rat anococcygeus smooth muscle.
The relationship between calcium concentration ([Ca2+]) and force in smooth muscle can be studied by permeabilizing the sarcolemma and bathing the preparation in a mock intracellular solution. Normally [Ca2+] 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]t) below 10 mM depresses Ca(2+)-activated force generated in 0.1 microM Ca2+. The observed threshold for the effect of EGTAt is 0.2 mM, and the effect is maximal at approximately 10 mM. BAPTA, another Ca2+ chelator, also produces this effect. Tension production in smooth muscle is controlled by acto-myosin 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 microM), an increase [EGTAt] 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.
Smith
G L
GL
Institute of Physiology, University of Glasgow, UK.
Crichton
C A
CA
D000818:Animals; D002118:Calcium / Q000378:metabolism / Q000494:pharmacology*; D004533:Egtazic Acid / Q000031:analogs & derivatives / Q000494:pharmacology*; D004789:Enzyme Activation / Q000187:drug effects; D009119:Muscle Contraction / Q000187:drug effects* / Q000502:physiology; D009130:Muscle, Smooth / Q000187:drug effects / Q000502:physiology*; D009219:Myosin-Light-Chain Kinase / Q000378:metabolism*; D051381:Rats; D017208:Rats, Wistar; D010738:Type C Phospholipases
D004533:Egtazic Acid; D009219:Myosin-Light-Chain Kinase; D010738:Type C Phospholipases; C025603:1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid; D002118:Calcium