Stimulation of Na+-Ca2+ exchange in cardiac sarcolemmal vesicles by proteinase pretreatment

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Abstract
The Na+-Ca2+ exchange activity of purified canine cardiac sarcolemmal vesicles can be strikingly stimulated if the vesicles are pretreated with a serine or thiol proteinase. The Km (Ca2+) for Na+i-dependent Ca2+ influx is reduced from 22.2 +/- 2.3 to 8.1 +/- 0.3 microM while Vmax is increased from 15.1 +/- 3.6 to 18.9 +/- 5.2 nmol Ca2+ . mg protein-1 . s-1. Na+o-dependent Ca2+ efflux is also stimulated by proteinase pretreatment although passive (Na+-independent) Ca2+ efflux from the sarcolemmal vesicles is unaffected. Proteinase treatment reduces the sensitivity of Na+-Ca2+ exchange to the inhibitors chlorpromazine and polymyxin B, but not to the inhibitor, palmitylcarnitine. Using a newly developed technique we are able to demonstrate that the Na+-Ca2+ exchange of inside-out sarcolemmal vesicles is being stimulated by proteinase treatment (Philipson, K. D., and A. Y. Nishimoto, J. Biol. Chem: 257, 5111-5117, 1982; this technique uses the ATP-dependent Na+ pump to preload only inside-out vesicles with Na+ prior to Na+-Ca2+ exchange). Right-side-out vesicles may also be stimulated.