Differential regulation of mu- and m-calpain in rat hearts perfused with Ca2+ and cAMP.
Reversible interconversion between calpastatin I and calpastatin II, the phosphorylated form of the inhibitor, has been induced in rat heart perfused with the combination Ca2+/A23187 ionophore or with cAMP. In the presence of the ionophore and increasing concentrations of Ca2+, calpastatin II is converted into calpastatin I; whereas the reverse reaction is induced by the addition of cAMP. Both interconversions leave substantially unmodified the amount of calpastatin I which inhibits mu-calpain with higher efficiency and accordingly keeps the proteinase in an permanent inactive state. On the contrary, expression of m-calpain activity is significantly repressed or alternatively largely augmented as a result of a profound increase or decrease in the level of calpastatin II induced by perfusion with cAMP or with Ca2+/ionophore respectively. Taken together our results demonstrate that bidirectional interconversion can take place in rat heart cells and through this mechanism the activity of m-calpain can be efficiently controlled. Ca2+ ions and cAMP are temptatively proposed as the natural stimuli responsible for the modulation of this overall process. Experimental evidences are provided indicating that the transition to the active form of mu-calpain involves association to the plasma membrane, a process competitively antagonized by calpastatin I; thus suggesting that interaction with one or the other ligand can affect the intracellular ratio between inactive and active mu-calpain forms.
Salamino
F
F
Institute of Biological Chemistry-University of Genoa, Italy.
De Tullio
R
R
Mengotti
P
P
Melloni
E
E
Pontremoli
S
S
D000818:Animals; D002118:Calcium / Q000494:pharmacology*; D002154:Calpain / Q000378:metabolism*; D002462:Cell Membrane / Q000378:metabolism; D000242:Cyclic AMP / Q000494:pharmacology*; D006321:Heart / Q000187:drug effects; D066298:In Vitro Techniques; D008297:Male; D009206:Myocardium / Q000378:metabolism*; D009281:Naphthalenes; D010766:Phosphorylation; D011083:Polycyclic Compounds / Q000378:metabolism; D051381:Rats
D009281:Naphthalenes; D011083:Polycyclic Compounds; C061464:calphostin I; D000242:Cyclic AMP; D002154:Calpain; D002118:Calcium