Cardiac glycoside receptors in cultured heart cells—I. characterization of one single class of high affinity receptors in heart muscle cells from chick embryos

Abstract

Abstrtlct-Bindin, of e H)-ouabain aod ouabain-induced inhibition of thc sodium pump and nf Ihe (Na" + K·}-ATPase have becn cbaracterized in cullurcd cardiac muscle aod Don musele cclls, as weil as in cardiac cell mcmbran~ll obtained from dUck embryos.

Cardiac glycoside binding sites in cultured heart muscle cells

“…The existence of one single class of binding sites in chicken heart cells, but of two classes in rat heart cells is further supported by different kinetics of ouabain binding process in these cells: in chicken heart cells, ( 3 H)-ouabain association follows second order, ouabain dissociation single first order reaction; the dissociation constant calculated from the rate constants being in good agreement with the one obtained from measurement of concentrationdependent ouabain binding under equilibrium conditions (22). In rat heart muscle cells, however, biphasic dissociation kinetics are present (table 1), the fast component being due to dissociation from the low affinity site (t 1/2 = 12 min at 37°).…”

“…This experimental evidence comes from both: measurement of ( 3 H)-ouabain binding under equilibrium condi tions, as well as kinetic studies of ( 3 H)-ouabain binding processes. Results obtained with cardiac cell membranes -prepared from the same tissues as cultured heart cells -further support the existence of different classes of ouabain binding sites in hearts from neonatal rats (22,23).…”

“…Mean values for dissociation constants and binding capacities are given in table 1. Cardiac non muscle cells have fewer binding sites than cardiac muscle cells, but with similar binding affinities for ouabain: also one class of sites is present in chicken cells, but two classes in rat cells (22,23).…”

“…Therefore, the existence of negative cooperativity of the binding sites can be excluded (3). Further characterization of ( 3 H)-ouabain binding reveals a strong temperature dependency, as tested for binding to the sites in chicken heart cells and to the high affinity sites in rat heart muscle cells (table 1); binding to these sites is strongly suppressed by potassium ions, while ouabain dissociation from these sites is not altered by K + (22,23).…”

“…We have used this established technique to characterize cardiac glycoside receptors in muscle and non muscle cells from both species (22,23). The present paper concentrates on the question: does the intact rat heart muscle cell in culture indeed possess two different classes of cardiac glycoside receptors?…”