Question

How does membrane fluidity effect how fast a signal travels?

Answer 1

Ans: Membrane fluidity (ordered, rigid state or in a relatively disordered, fluid state) depends primarily on the length of the fatty acid side chains and their degree of unsaturation and cholesterol content. In other words fluidity mainly depends on the ratio of phospholipids to cholesterol content. Cholesterol (appropriate amount, excess leads to rigidity) plays a vital moderating role in not fully rigidifying or not fully fluidic membrane. Fluidity also depends on the temperature, pH, pressure etc. This fluidity in turn affects the mobility of proteins across the membrane; remember most of the receptors are proteins involved in the signal transduction. Another complexity proposal of a lipid rafts, these are the regions rich in saturated glycosphingolipids, more cholesterol than normal plasma membrane and protein receptors for a glycoprotein microdomains forming lipid rafts (like a floating wood/bamboo rafts on a river of plasma membrane). They are little tighter or less fluid than the plasma membrane. But existence of lipids rafts is still a controversial subject

Here signal means first we will discuss relation between membrane fluidity and signal transduction. Generally as fluidity increases (more unsaturated lipids more sterols and less cholesterol) signal transduction increases up to point because transducing protiens can move laterally with increased speed. Generally as fluidity decreases (more saturated lipids, less sterol and more cholesterol) signal transduction decreases up to point because transducing protiens cannot move laterally with increased speed because of the stiffness of the plasma membrane. Now comes in to the picture ‘lipid rafts’ are regions not majorly affected or minorly affected by the overall fluidity of the membrane due to dynamic changing conditions so that signal processing does not affect.

Coming to nerve conduction calcium ions play an important role as second messengers. In the plasma membrane long chain fatty acids acting at lipid specific sites near the channel or directly on the protein channel itself play a role in activating calcium channels. We can conclude that for nerve signals will be proper/faster if membrane fluidity is/should be on rigid side.