Ouabain-insensitive, Na(+)-stimulated ATPase activity in rabbit cardiac sarcolemma.

The rabbit cardiac sarcolemma shows an ouabain, Na,K-stimulated ATPase activity and an ouabain-insensitive, Na-stimulated ATPase activity. The Na-ATPase has the following characteristics: (i) It is also stimulated by other monovalent cations. (ii) It is inhibited by 2 mM Furosemide and by 2 mM ethacrynic acid. (iii) It reaches maximal values (Vmax) at around 20 mM Na+. (iv) The apparent Km is around 5 mM. Except for the monovalent cation stimulation, the main characteristics of this ATPase are very similar to those of the ouabain-insensitive, Na-stimulated ATPase of mammalian kidneys.