Figure 2.

PDBu inhibits or stimulates the transport activity of Na, K-ATPase in COS-7 cells incubated at 37 and 18°C, respectively. Na,K-ATPase-mediated ⁸⁶Rb uptake was measured under initial rates of influx in nontransfected (NT) COS-7 cells or in cells stably expressing the wild-type (WT) Bufo α1 subunit. In transfected cells, ⁸⁶Rb uptake was determined in the presence of 2.5 × 10⁻⁶ M ouabain, which completely inhibits the endogenous Na, K-ATPase. Cells were incubated without (C, open bars) or with 10⁻⁷ M PDBu (P, filled bars) for 15 or 30 min in experiments performed at 37°C (upper panel) and 18°C (lower panel), respectively. Results are expressed as picomoles of Rb (K) × minute⁻¹ × microgram of protein⁻¹ and are means ± SE from 7–20 independent experiments (*, p < 0.05; **, p < 0.01).