Phosphorylation of the alpha subunit enhances pump activity, presumably by increasing turnover rate or affinity for substrates. A number of hormones stimulate kinase or phosphatase activities within the cell that affect pump activity. Also, it appears that some cell types contain an intracellular pool of pumps that can be rapidly recruited to a functional state in the plasma membrane. Chronic or sustained changes in pump activity within cells is usually due to increases in transcription rate or mRNA stability. This effect appears to result from stimulation of subunit gene transcription.
Aldosterone is a steroid hormone with major effects on sodium homeostasis.
It stimulates both rapid and sustained increases in pump numbers within several tissues. The sustained effect is due to enhanced transcription of the genes for both subunits. Catecholamines have varied effects, depending on the specific hormone and tissue. These effects seem to be mediated via phosphorylation or dephosphorylation of the pumps. Insulin is a major regulator of potassium homeostasis and has multiple effects on sodium pump activity.