The apparent discrepancy of ouabain inhibition of cation transport and of lymphocyte proliferation is explained by time-dependency of ouabain binding
✍ Scribed by George B. Segel; Marshall A. Lichtman
- Publisher
- John Wiley and Sons
- Year
- 1980
- Tongue
- English
- Weight
- 403 KB
- Volume
- 104
- Category
- Article
- ISSN
- 0021-9541
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✦ Synopsis
Abstract
Mitogenesis of human blood lymphocytes in culture is inhibited by concentrations of ouabain that are approximately one order of magnitude lower than those that block Na and K transport. For example, the 50% inhibition (ID~50~) of Na‐K transport, 280 nM, is seven‐fold greater than the ID~50~ for RNA synthesis, DNA synthesis, or blastogenesis, ˜40 nM. Yet, inhibition of transport and consequent reduction in cell K is considered responsible for the effects of ouabain on mitogenesis. Since synthetic processes are assessed at least 24 hours after lymphocyte stimulation, this discrepancy could be explained by either 1) a progressive increase in K leak, or 2) a progressive inhibition of Na‐K transport by ouabain during 24 hours of PHA treatment. We found that the lymphocyte membrane leak rate of K increased immediately after PHA treatment but did not increase further from 4 to 24 hours. In contrast, the ouabain sensitivity of ^42^K uptake was markedly increased with time: ID~50~ for ^42^K uptake of 35 nM at 24 hours as compared to 280 nM at 30 minutes. Measurement of ouabain binding revealed a seven‐fold increase in the lymphocyte‐associated ouabain after 24 hours compared to binding at 1 hour. These data indicate that the dose response of ouabain inhibition of active K transport and lymphocyte proliferation are closely correlated if one considers the slow membrane binding of ouabain at low concentrations.