**5.2. Modulation of neuronal plasma membrane Na+-K+-ATPase specific activity as a function of specific binding of L-triiodothyronine in adult rat brain cerebrocortical synaptosomes**

Subsequently the idea of concentration, distribution and metabolism of THs within the mature brain generated interest to search for potential role of TH and its nongenomic interaction, if any, with neuronal plasma membrane. TH is well known for its regulation of energy metabolism in developing tissues including brain. However, adult brain has not shown this effect on energy metabolism under the influence of TH until recently. Maintenance of ionic gradients by plasma membrane Na+-K+-ATPase (NKA) is one of the important cellular events by which TH regulate energy metabolism. NKA is an ion pump responsible for maintaining Na+ and K+ ion gradients across the cellular plasma membrane in eukaryotic cells. The Na+ and K+ ion gradients are important for establishment of resting membrane potentials as well as for transport of certain molecules. NKA has special significance in maintaining membrane potentials in neurons. Inhibition of NKA has been shown to release acetylcholine [43] and norepinephrine [44] from rat cortical synaptosomes, presumably as a result of depolarizing effects of lowered K+ gradients. The level of NKA activity could therefore have consequence for the regulation of the neurotransmitter release and uptake across the synaptic membrane [43].
