Figure 10.
The effects of DHO on Na/K pump current in human heart cells. Stimulation of IP by low [DHO] and inhibition of IP by high [DHO] were observed in human ventricular myocytes (A) and in human atrial myocytes (B). (C) The effects of β-adrenergic activation (ISO) and α-adrenergic activation (NE + PROP) on IP in human atrial cells. Bars indicate standard deviations. The numbers in the parentheses represent the number of cells studied. There was no significant effect of ISO (P = 0.50). However, there was a significant difference between IP in control and that in the presence of α-adrenergic activation (P = 0.009). (D) The ΔIP-DHO curve in human atrial cells. ΔIP was normalized as described in Fig. 6 A. Data were fitted assuming the presence of only one DHO affinity pump, since the α1-isoform of the Na/K pump in human heart has essentially the same DHO affinity as the α2- and α3-isoforms. The positive values of ΔIP at DHO concentrations of 10−9, 10−8, and 10−7 M represent statistically significant increases in the holding current with P values of 3 × 10−3, 10−3, and 4 × 10−3, respectively.