There are 4 classes of potassium membrane channels

Who would have thought that I owe wikipedia for today's 'Wow!' moment that there are 4 major classes of potassium membrane channels.

Significance?

This is such a wonderful finding because my learning about resting and action membrane potentials makes much more sense. More specifically, I know that two different classes of potassium channels are responsible for the resting and for the action membrane potential, which is something I suspected and now have in writing :)

So the resting membrane potential of a typical neuron is negative (close to -60mV) because the membrane is more permeable to potassium ions at rest via the tandem pore domain potassium channels. Therefore, at rest, the positive potassium ions leave the neurons down the electrochemical gradient making the inside of the neurons more negative.
Of note, if the membrane of the resting neuron was more permeable to sodium ions than to potassium ions, the resting membrane potential would be much more positive (e.g. +40mV) because the positive sodium ions would enter the neuron down their electrochemical gradient.

On the other hand, when an action potential arrives, the membrane becomes relatively more permeable to sodium than to potassium ions via opening of voltage-gated sodium channels. As then the positive sodium ions enter the neurons, making the membrane potential more positive (e.g. +40mV).

When the membrane (action) potential reaches a treshold voltage (e.g. +40mV), the membrane again becomes relatively more permeable to potassium ions and less to sodium ions. Now the voltage-gated potassium channels open and allow the positive potassium ions out of the neuron making the membrane potential more negative again.

In the refractory period the membrane is more permeable to potassium ions and the ion concentrations inside and outside of the cell normalise back to the baseline of the resting membrane potential.

Well, I am stil learning so I suspect the above is still too basic at best and plain wrong at worst.

Membrane capacitance to measure vesicular release

My notes are based on a very old paper by Angelson & Betz (1997). I am not sure how much relevance it still has today. So keep that in mind.

Membrane capacitance
- capacitance of a membrane can be used to measure exocytosis/endocytosis, vesicular release and neurotransmitter release

- because as vesicles fuse with the membrane, its area and volume increase and it is able to 'store' more charge (explained here)

- however, this can be done well only with vesicles larger than 50 nm in diameter so apparently not that many...

- also, for this technique whole-cell clamp is less useful than perforated-cell clamp and than on-cell clamp

A method of finding unknown proteins of a specific function

...by creating an artificial protein of this specific function of interest.

I know it is not so much related to appetite regulation but I still think it's cool!

Details
In cellular biology, scientists can design an artificial protein structure. Then they can go and look into 100,000s let's say yeast colonies and see what mutant cells can't exist without this protein structure. When they find these mutants, saved by the protein, they can see what the mutant gene/protein is and go on and fully characterise it.

So simply by designing an artificial protein structure of a known function, endogenous proteins of this same functionality can be find and characterised.

Reference: http://www.sciencemag.org/content/325/5939/477.abstract Kornmann et al., 2009. An ER-Mitochondria Tethering Complex Revealed by a Synthetic Biology Screen. Science, 325(5939), 477-481.

How is the brain important for the regulation of appetite?

We know that maintaining energy balance is essential for keeping a healthy weight i.e. for not developing obesity with all its negative consequences on our life expectancy and mental and physical health.

We also know that brain is a key organ which regulates the energy balance.

But what evidence do we have that convinces us that it is specifically the brain that is the key regulator of energy balance?

There are many lines of evidence which establish the brain, in particular the hypothalamus, as the key regulator of energy balance. However, among the most convincing examples are probably genetic studies of some of the most common monogenic causes of human obesity.

These studies link specific proteins to brain circuits responsible for the regulation of energy balance, specifically to the hypothalamic leptin–melanocortin signalling pathway (see the figure).

In this pathway, leptin, which is secreted from the adipose tissue in proportion to the size of the fat deposits, stimulates leptin receptors on proopiomelanocortin (POMC)-expressing neurons in the arcuate nucleus of the hypothalamus (ARC), a key site of central regulation of energy balance. Subsequently, prohormone convertase 1 (PC1) cleaves the POMC protein into α and β melanocyte stimulating hormones (MSHs). MSHs stimulate melanocortin 4 receptors (MC4Rs), expressed exclusively in the brain, to ultimately reduce food intake and increase energy expenditure.

Deficiency in these components of the pathway – namely leptin, leptin receptor (LepR), pro-opiomelanocortin (POMC), prohormone convertase 1 (PC1), melanocyte stimulating hormone (MSH) and melanocortin 4 receptor (MC4R) – result in positive energy balance and consequently in obesity (Montague et al., 1997; Clement et al., 1998; Krude et al., 1998; Jackson et al., 1997; Yeo et al., 1998).


Figure legend: Most common human monogenetic causes of obesity are linked to the brain, supporting the role ot the brain in the regulation of energy balance. Protein deficiencies resulting in human monogenetic obesity are highlighted in red (adapted from Oswald and Yeo, 2007).

Electrophysiology for dummies alias what is fast capacitance, slow capacitance and R-series?

As I promised yesterday, some basic electrophysiology knowledge is coming next as I'm currently learning this technique.

Slow capacitance (C-slow)
- can be viewed as the storage of charge in a cellular (in this case neuronal) membrane
- by pressing the ''Auto'' button in PatchMaster, it is subtracted from the recording for a more accurate result
- it is based on the size of the cell, therefore, on the size of the cell's membrane
- therefore, we can't do much about slow capacitance (can't decrease it)
- therefore, scientists focus on decreasing the fast capacitance to improve the recordings

Fast capacitance (C-fast)
- can be viewed as the storage of charge in a pipette (which is used to patch on cells)
- likewise, by pressing the ''Auto'' button in PatchMaster, it is subtracted from the recording for a more accurate result
- can be improved (decreased) by changing the properties of the pipette (e.g. coating the pipette)

R-series
= series resistance
- therefore measured in ohms
- can be viewed as resistance to the flow of current which is measured in the cell and in the contents of the pipette (their contents mix during whole cell patching and that's why we fill the pipette with an intracellular solution, i.e. one that mimicks the contents of the cell)
- on part of the pipette, the flow is blocked by the pipette's diameter; and on part of the cell, the flow is blocked by the contents of the cell such as the nucleus and other organelles
- we try to have the resistance of the tip and the cell as low as possible for ideal recordings

c-Fos as a marker of neuronal activation - pluses & minuses

Yes, I know, c-Fos for the third time! But bear with me because a new exciting topic of electrophysiology will be coming shortly as I'll be learning that technique.

c-Fos or other markers used in our lab?

In our lab, we haven't used any other markers of neuronal activation (despite researching this alternative last year). Other markers crop up in papers from time to time but c-Fos is best established and most widely used in our field and therefore, works best for our purposes.


Still, what are the pluses & minuses of using c-Fos as a marker of neuronal activity?

+ c-Fos marks recently active neurons

+ can be used together with physiology research and immunohistochemistry techniques

+ is best established and most widely used in our field so we can compare our results with other people's results

- it isn't a direct marker of neuronal activity

- some neurons may be acitvated but c-Fos doesn't have to be transcribed and translated i.e. c-Fos isn't in a pathway for all stimuli/responses

- time course of c-Fos expression might differ cell-to-cell and response-to-response so it needs to be established individually for each experiment

Neurons in the brain are like stars in the universe

At least for me and at least in this youtube video :)

http://www.youtube.com/watch?v=90cj4NX87Yk&feature=related

Also, I like the part where the animation shows the exchange of the ions.