The Na(+)-dependence of Na(+)-activated K(+)-channels (IK(Na)) in guinea pig ventricular myocytes, is different in excised inside/out patches and cell attached patches.

Single Na(+)-activated K(+)-channels were recorded from intact guinea-pig ventricular myocytes perfused with Ca-free, Mg-free Tyrode, to increase [Na+]i. The activity of these channels increases with the time of perfusion with this solution and decreases when the bathing sodium is reduced. The activity of the Na(+)-activated K(+)-channel is greater in the cell attached patches than from excised cell free patches, at the same [Na+]. It is suggested that this K+ channel is significantly active in intact cells within the physiological range of [Na]i.