Does Binding of Ouabain to Human α1-Subunit of Na⁺, K⁺-ATPase Affect the ATPase Activity of Adjacent Rat α1-Subunit?

抄録

To ascertain whether ouabain binding to human α1-subunit influences coexpression of rat α1-subunit, the ouabain-sensitive profiles of Na⁺, K⁺-ATPase activity and ⁸⁶Rb⁺ uptake activity and ouabain binding capacity were measured in HeLa cells stably expressing rat α1-subunit. The ouabain-sensitive profile of ATPase and ⁸⁶Rb⁺ uptake activity seemed to be the sum of two components, one with high and one with low apparent affinity to ouabain, which were similar to that observed in HeLa and NRK-52E cells derived from human and rat, respectively. The ATPase activity with low sensitivity to ouabain increased in simple proportion to the amount of the rat α1 mRNA derived from transfected cDNA, which was determined by the reverse transcription-polymerase chain reaction method. The turnover number of the human Na⁺, K⁺-ATPase activity obtained from the ratio of the Na⁺, K⁺-ATPase activity to the ouabain binding capacity is about 150/sec. The expression of the rat α1-subunit had no effect on the turnover numbers of the Na⁺, K⁺-ATPase activity with high affinity to ouabain estimated from the ouabain binding capacity as the active site concentration. These results suggested that the ouabain bound to human α1-subunit did not inhibit the ATPase activity of the coexpressing rat α1 in these cells.