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Am J Physiol Cell Physiol 265: C1118-C1127, 1993;
0363-6143/93 $5.00
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AJP - Cell Physiology, Vol 265, Issue 4 C1118-C1127, Copyright © 1993 by American Physiological Society

ARTICLES

Alpha-chymotrypsin deregulation of the sodium-calcium exchanger in barnacle muscle cells

R. Espinosa-Tanguma, J. DeSantiago and H. Rasgado-Flores
Department of Physiology and Biophysics, University of Health Sciences Chicago Medical School, Illinois 60064.

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.


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M. P. Blaustein and W. J. Lederer
Sodium/Calcium Exchange: Its Physiological Implications
Physiol Rev, July 1, 1999; 79(3): 763 - 854.
[Abstract] [Full Text] [PDF]


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