Shrinkage-induced activation of Na+/H+ exchange in primary rat astrocytes: role of myosin light-chain kinase

Am J Physiol. 1995 Jul;269(1 Pt 1):C257-66. doi: 10.1152/ajpcell.1995.269.1.C257.


Primary rat astrocytes exposed to hyperosmotic solutions undergo Na(+)-dependent amiloride-sensitive alkalinization of 0.36 U [measured with the pH-sensitive fluorescent dye 2',7'-bis(carboxyethyl)-5(6)-carboxy-fluorescein], suggesting that shrinkage-induced alkalinization is due to activation of Na+/H+ exchange (NHE). Alkalinization is maintained for at least 20 min, and is readily reversible and ATP dependent. Hyperosmotic solutions produced no increase of intracellular Ca2+ or adenosine 3',5'-cyclic monophosphate (cAMP). Loading cells with 1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid, a Ca2+ chelator, or depleting cells of protein kinase C (PKC) had no effect on activation of NHE. Thus shrinkage-induced activation of NHE does not involve cAMP, Ca2+, or PKC. However, ML-7, an inhibitor of myosin light-chain kinase (MLCK), inhibited shrinkage-induced activation with a half-maximal inhibition of 56 microM. This activation was also inhibited by 500 microM N-(6-aminohexyl)-5-chloro-1-naphthalenesulfonamide, 100 microM chlorpromazine, and 50 microM trifluoperazine, all calmodulin inhibitors. Shrinkage increased the phosphorylation of an 18-kDa protein that colocalizes with myosin light chain. Our data suggest that shrinkage-induced activation of NHE in astrocytes occurs via a novel pathway involving activation of calmodulin-dependent MLCK and phosphorylation of myosin light chain.

Publication types

  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, Non-P.H.S.
  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Adenosine Triphosphate / physiology
  • Animals
  • Astrocytes / cytology
  • Astrocytes / metabolism*
  • Calcium / physiology
  • Calmodulin / antagonists & inhibitors
  • Cells, Cultured
  • Cyclic AMP / physiology
  • Myosin-Light-Chain Kinase / physiology*
  • Phosphorylation
  • Protein Kinase C / physiology
  • Rats
  • Rats, Sprague-Dawley
  • Sodium-Hydrogen Exchangers / metabolism*


  • Calmodulin
  • Sodium-Hydrogen Exchangers
  • Adenosine Triphosphate
  • Cyclic AMP
  • Protein Kinase C
  • Myosin-Light-Chain Kinase
  • Calcium