Alpha-chymotrypsin deregulation of the sodium-calcium exchanger in barnacle muscle cells.
To gain insight into the mechanism by which the protease alpha-chymotrypsin (alpha-chym) activates the Na-Ca exchanger in muscle cells we studied 1) the ability of this enzyme to remove the intracellular "catalytic" Ca2+ requirement for activation of all the modes of exchange mediated by the Na-Ca exchanger (i.e., Nao-Cai, Nai-Cao, Nao-Nai, and Cao-Cai, where the subscripts o and i represent extracellular and intracellular, respectively), and 2) the ability of certain monovalent cations to stimulate Cao-Cai exchange after activation of the exchanger by alpha-chym. Barnacle muscle cells were used as models because these cells are so large that they can be internally perfused and voltage clamped. The results show that alpha-chym produces a highly activated Na-Ca exchanger able to operate in all its modes of exchange independently of catalytic Cai. The concentration-dependent effect of alpha-chym was biphasic; maximal activation occurred at 0.5 mg alpha-chym/ml perfusate for 20 min of perfusion at a perfusion rate of 2.5 microliters/min. The results are discussed in terms of the possible effects of alpha-chym on the kinetic modulation of the exchanger.
Espinosa-Tanguma
R
R
Department of Physiology and Biophysics, University of Health Sciences Chicago Medical School, Illinois 60064.
DeSantiago
J
J
Rasgado-Flores
H
H
D000818:Animals; D002118:Calcium / Q000378:metabolism; D002352:Carrier Proteins / Q000378:metabolism*; D002414:Cations, Monovalent / Q000494:pharmacology; D002918:Chymotrypsin / Q000494:pharmacology / Q000502:physiology*; D007474:Ion Exchange; D009132:Muscles / Q000166:cytology / Q000378:metabolism* / Q000502:physiology; D012964:Sodium / Q000378:metabolism; D019831:Sodium-Calcium Exchanger; D001468:Thoracica
D002352:Carrier Proteins; D002414:Cations, Monovalent; D019831:Sodium-Calcium Exchanger; D012964:Sodium; D002918:Chymotrypsin; D002118:Calcium