Effects of Ouabain on Proliferation of Human Endothelial Cells Correlate with Na⁺,K⁺-ATPase Activity and Intracellular Ratio of Na⁺ and K⁺

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A. M. Tverskoi¹, S. V. Sidorenko¹, E. A. Klimanova¹, O. A. Akimova¹, L. V. Smolyaninova¹, O. D. Lopina¹, and S. N. Orlov^1,2,3*

¹Lomonosov Moscow State University, Faculty of Biology, 119991 Moscow, Russia; E-mail: sergeinorlov@yandex.ru

²Tomsk National Research State University, 634050 Tomsk, Russia

³Siberian State Medical University, 634050 Tomsk, Russia

^* To whom correspondence should be addressed.

Received March 10, 2016; Revision received May 3, 2016

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Side-by-side with inhibition of the Na⁺,K⁺-ATPase ouabain and other cardiotonic steroids (CTS) can affect cell functions by mechanisms other than regulation of the intracellular Na⁺ and K⁺ ratio ([Na⁺]_i/[K⁺]_i). Thus, we compared the dose- and time-dependences of the effect of ouabain on intracellular [Na⁺]_i/[K⁺]_i ratio, Na⁺,K⁺-ATPase activity, and proliferation of human umbilical vein endothelial cells (HUVEC). Treatment of the cells with 1-3 nM ouabain for 24-72 h decreased the [Na⁺]_i/[K⁺]_i ratio and increased cell proliferation by 20-50%. We discovered that the same ouabain concentrations increased Na⁺,K⁺-ATPase activity by 25-30%, as measured by the rate of ⁸⁶Rb⁺ influx. Higher ouabain concentrations inhibited Na⁺,K⁺-ATPase, increased [Na⁺]_i/[K⁺]_i ratio, suppressed cell growth, and caused cell death. When cells were treated with low ouabain concentrations for 48 or 72 h, a negative correlation between [Na⁺]_i/[K⁺]_i ratio and cell growth activation was observed. In cells treated with high ouabain concentrations for 24 h, the [Na⁺]_i/[K⁺]_i ratio correlated positively with proliferation inhibition. These data demonstrate that inhibition of HUVEC proliferation at high CTS concentrations correlates with dissipation of the Na⁺ and K⁺ concentration gradients, whereas cell growth stimulation by low CTS doses results from activation of Na⁺,K⁺-ATPase and decrease in the [Na⁺]_i/[K⁺]_i ratio.

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KEY WORDS: proliferation, endothelium, Na⁺,K⁺-ATPase, ouabain, intracellular Na⁺ and K⁺

DOI: 10.1134/S0006297916080083

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