Another Na+/K+-ATPase regulatory mechanism!

Recently, I have started writing the introduction of my thesis. Since my project is mostly involving Na+/K+-ATPase in locusts, I've planned to dedicate a substantial section of my introduction to talk about on the general background of the Na+/K+-ATPase. As I was looking through past studies for ATPase backgrounds, I've came across this paper that introduced another regulating mechanism on the Na+/K+-ATPase.

As people know, unlike tropical animals, sub-arctic organisms and poikilotherms such as insects, would have to overcome difficult winters annually. Through evolution, those animals have come up with different strategies to withstand the cold winter to ensure their survival. One of strategies the animals utilize is diapause (a hypometabolic state of arrested development). During this state, animals often suppress most of their metabolic processes and leaving on only the essential pathways to minimize ATP expenditure. As one of the most energy-expensive protein, the Na+/K+-ATPase which consumes 5 to 40% of a cell’s energy, has to be regulated during the diapause if the organism is to survive winter.

 

The researchers in this paper has found that the Na+/K+-ATPase activity can be reversibly suppressed by Protein Kinase A, C and G during winter to a point where only a fraction of the control activities were exhibited. Sequentially, the ATPase activity can be restored back to its normal state using a phosphate.

In this study, the researchers examined the Na+/K+-ATPase activity from the galls containing last instar larvae of Eurosta solidaginis. The researchers studied the ATPase activity during different winter months, as well as the effects of kinases on the ATPase. To study the ATPase winter activity, researchers assessed its activity in different sets of animals in October, November, January, February and April. They found that the ATPase activity was significantly lower in November and January with respect to October. Nonetheless, the ATPase activity recovered in February, and further enhaced in April.

This image illustrated that the Na+/K+-ATPase is siginificantly lowered in Nov., and Jan. with respect to Oct. However, the activity in restored in Feb., and further enhanced in April.

This figure illustrated that the Na+/K+-ATPase inhibition caused by PKA, PKC and PKG can be restored using a calf-intestinal alkaline phosphatease (CIAP).

In addition, when researchers studied the ATPase activity under the presence of PKA, PKC and PKG, they found that the kinases cause the ATPase activity to decrease to just 3 to 8% of the control values. However, the activity can be restored through the addition of a phosphatase.

This paper illustrated that during winter months, diapausal organisms can easily reduce their most ATP-consuming process, the Na+/K+-ATPase, by reversible phosphorylation via PKA, PKC and/or PKG. Once spring comes around, the animals can easily restore their ATPase activity via a phosphatase. The results from this study could suggest a biochemical pathway that could easily be utilized by other hibernating animals to conserve their ATP. In addition, the results from this paper also added to the general pool of knowledge of winter metabolic suppression.

Lastly, the parts I did not like about this experiments is that the researchers did not examine the activities of PKA, PKC and PKG during the winter months to prove that the activity decrease observed in winter months was actually due to the kinases. Furthermore, another area I was confused about this paper was that the effect that all the controls had a ‘non-1’ normalized value, which is normally impossible.

Reference: McMullen, D.C., Storey, K.B., 2008. Suppression of Na+/K+-ATPase activity by reversible phosphorylation over the winter in a freeze-tolerant insect. Journal of Insect Physiology 54:1023-1027