Profound regulation of Na/K pump activity by transient elevations of cytoplasmic calcium in murine cardiac myocytes

Abstract

Small changes of Na/K pump activity regulate internal Ca release in cardiac myocytes via Na/Ca exchange. We now show conversely that transient elevations of cytoplasmic Ca strongly regulate cardiac Na/K pumps. When cytoplasmic Na is submaximal, Na/K pump currents decay rapidly during extracellular K application and multiple results suggest that an inactivation mechanism is involved. Brief activation of Ca influx by reverse Na/Ca exchange enhances pump currents and attenuates current decay, while repeated Ca elevations suppress pump currents. Pump current enhancement reverses over 3 min, and results are similar in myocytes lacking the regulatory protein, phospholemman. Classical signaling mechanisms, including Ca-activated protein kinases and reactive oxygen, are evidently not involved. Electrogenic signals mediated by intramembrane movement of hydrophobic ions, such as hexyltriphenylphosphonium (C6TPP), increase and decrease in parallel with pump currents. Thus, transient Ca elevation and Na/K pump inactivation cause opposing sarcolemma changes that may affect diverse membrane processes.DOI: http://dx.doi.org/10.7554/eLife.19267.001

Regulation of ion transport from within ion transit pathways

“…5, A and B, we studied Na/K pump function in mouse myocytes using half-maximal cytoplasmic Na concentrations and attempted to identify factors that might regulate pump activity. Surprisingly, from many classical signaling mechanisms examined, we found that in mouse myocytes, cytoplasmic Ca elevation caused the largest regulatory increases of Na/K pump activity (Lu et al, 2016). Fig.…”

“…Accordingly, we suggested that pumps tend to inactivate (state 5 to state 6 transition) when they are oriented to the cytoplasmic side (i.e., in E 1 configuration) and their binding sites are not fully occupied by Na. We cannot exclude a possibility that cytoplasmic K binding may contribute to inactivation by forcing pumps backward in the cycle into stable K-occluded states, but cytoplasmic K is with good certainly not required for inactivation (Lu et al, 2016).…”

“…The physiological “sense” of this regulatory process is that cells will maintain a substantial fraction of their pumps as a pump reserve in an inactive state that can be recruited for active transport as needed when cytoplasmic Na begins to rise. The inactivation mechanism remains pronounced, but is less strong, in myocytes that lack the “gamma subunit” of Na/K pumps in muscle, phospholemman (Lu et al, 2016). In this light, it would be of great interest to know whether other FXYD proteins might support Na/K pump inactivation and whether they might become more important in phospholemman-knockout mice.…”

“… Na/K pump currents in a mouse myocyte, recorded as described previously ( Lu et al, 2016 ). (A) Whole-cell recording of pump current with 20 mM cytoplasmic Na and 7 mM extracellular Na.…”

Effect of salinity on modulation by ATP, protein kinases and FXYD2 peptide of gill (Na+, K+)-ATPase activity in the swamp ghost crabUcides cordatus(Brachyura, Ocypodidae)

“…However, in cells transfected with Ser23 to Ala23 α1-mutants, the (Na + , K + )-ATPase cannot be phosphorylated by PKC (Poulsen et al, 2010). Phosphorylation of rat (Na + , K + )-ATPase α-subunit by an endogenous Ca 2+ /calmodulin-dependent protein kinase (CaMK) inhibits catalytic activity significantly (Netticadan et al, 1997) and constitutes part of a mechanism mediating Ca 2+ effects on the enzyme (Yingst et al, 1992; Lu et al, 2016).…”