Summary
It has recently been demonstrated that both Tl+ and Li+ produce concentration-and time-dependent positive inotropic effects in guinea-pig atrial preparations although Tl+ inhibits and Li+ stimulates isolated Na+, K+-ATPase in vitro. In order to elucidate the mechanism of the positive inotropic actions of these cations, the effects of Tl+ and Li+ on sodium pump activity were studied. Active 86Rb uptake in guinea-pig ventricular slices, an estimate of sodium pump activity, was highly sensitive to the inhibitory effect of the cardiac glycosides. Preincubation of slices with Tl+ caused a dose-and time-dependent inhibition of active 86Rb uptake. Similar concentration-and time-dependent inhibition of active 86Rb uptake was observed when Na+ in a Krebs-Henseleit solution was partially replaced with Li+. Lithium, however, stimulated a partially purified Na+, K+-ATPase in vitro. During heart slice incubation, Tl+ and Li+ accumulated in a time-dependent manner. This accumulation was not readily reversible when slices were transferred into Tl+-or Li+-free solutions. It appears that the inhibition of sodium pump activity is related to the positive inotropic action of these cations.
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Ku, D.D., Akera, T., Olgaard, M.K. et al. Effects of lithium and thallous ions on sodium pump activity in the guinea-pig heart and their relationship to the positive inotropic action. Naunyn-Schmiedeberg's Arch. Pharmacol. 304, 167–173 (1978). https://doi.org/10.1007/BF00495553
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DOI: https://doi.org/10.1007/BF00495553