The Fall of the Membrane Theory: Uncovering the Truth Behind the Na+/K+ Pump

[Simfish]

Okay, if the cell's cytoplasm has a net ionization charge of -1 (efflux of 3 Na+; influx of 2 K+), then why doesn't it just do a net efflux of a positively charged ion to maintain it for sake of osmotic balance? Well hm, it needs to efflux those ions SOMEHOW, But there aren't a lot of reactions producing Na+ as a waste product - where does the cell get all its Na+ from? (the Na+ that it wants to efflux out of the cell). Yes it is a deliberate way to maintain SOME gradient in a way such that Na+ atoms naturally influx into the cell (and drag glucose atoms along with them). But can't the same thing be done if the cell has way too many K+ ions relative to the bloodstream? (in which case some other ion, like a Cl- ion, might get attracted).

 

[kingdomof]

The cell doesn't have a net ionization -1. It's potential is given by the Nernst-Goldman Equation: http://www.nernstgoldman.physiology.arizona.edu/

Na+ is constantly diffusing across the cell membrane as is K+ through ion channels and other mechanisms.

And yes, reversing the Na+/K+ gradients can achieve the same effect; this is how the hair cells in the cochlea work.

Furthermore, the charge experienced at any point by a transporter or pump is phenomenological (think about it, the ions aren't in uniform distribution throughout the cytoplasm or interstitial fluid); this is the reason why we are able to flex our finger rapidly without stopping without somehow entering a refractory period, preventing this action, too swiftly, and it is also the reason how an action potential is able to propagate down an axon. With that idea discussed, think about the idea behind the movement of K+ and Na+ to create their respective electrochemical gradients; not only do you have a gradient that can be exploited to transport things into the cell, but you also have a gradient that may allow export. A lot of cotransport takes place depending on the type of cell and what its purposes are. It just so happens Na+ and K+ are the concentrations they are in most cells; there are exceptions, however, I do not know their functional implications, but I highly doubt there would be any.

More food for thought: the sizes of these respective ions are unique and therefore they need different ion channels to diffuse through.

Hope I helped.

 

[somasimple]

Na+ is constantly diffusing across the cell membrane as is K+ through ion channels and other mechanisms.

http://www.biology-online.org/dictionary/Cytoplasm

Cytoplasm

Definition

noun

(Science: Cell Biology)

In eukaryotic cells, the cytoplasm is that part of the cell between the cell membrane and the nuclear envelope. It is the jelly-like substance in a cell that contains the cytosol, organelles, and inclusions, but not including the nucleus. In fact, the cytoplasm and the nucleus make up the protoplasm of a eukaryotic cell.

In prokaryotic cells that do not have a well-defined nucleus, the cytoplasm is simply everything enclosed by the cell membrane. It therefore contains the cytosol, and all the other cellular components, including the chromosome in the nucleoid region.

Free diffusion of ions in a jelly? Really...

 

[somasimple]

Physiol Chem Phys Med NMR. 2007;39(1):1-67.


History of the membrane (pump) theory of the living cell from its beginning in mid-19th century to its disproof 45 years ago--though still taught worldwide today as established truth.

Ling G.

Damadian Foundation for Basic and Cancer Research, USA. gilbertling@dobar.org

The concept that the basic unit of all life, the cell, is a membrane-enclosed soup of (free) water, (free) K+ (and native) proteins is called the membrane theory. A careful examination of past records shows that this theory has no author in the true sense of the word. Rather, it grew mostly out of some mistaken ideas made by Theodor Schwann in his Cell Theory. (This is not to deny that there is a membrane theory with an authentic author but this authored membrane theory came later and is much more narrowly focussed and accordingly can at best be regarded as an offshoot of the broader and older membrane theory without an author.) However, there is no ambiguity on the demise of the membrane theory, which occurred more than 60 years ago, when a flood of converging evidence showed that the asymmetrical distribution of K+ and Na+ observed in virtually all living cells is not the result of the presence of a membrane barrier that permits some solutes like water and K+ to move in and out of the cell, while barring--absolutely and permanently--the passage of other solutes like Na+. To keep the membrane theory afloat, submicroscopic pumps were installed across the cell membrane to maintain, for example, the level of Na+ in the cell low and the level of K+ high by the ceaseless pumping activities at the expense of metabolic energy. Forty-five year ago this version of the membrane theory was also experimentally disproved. In spite of all these overwhelming evidence against the membrane-pump theory, it still is being taught as verified truth in all high-school and biology textbooks known to us today. Meanwhile, almost unnoticed, a new unifying theory of the living cell, called the association-induction hypothesis came into being some 40 years ago. Also little noticed was the fact that it has received extensive confirmation worldwide and has shown an ability to provide self-consistent interpretations of most if not all known experimental observations that are contradicting the membrane-pump theory as well as other observations that seem to support the membrane pump theory.

Publication Types:

* Historical Article


PMID: 18613639 [PubMed - indexed for MEDLINE]