Cell Communication (Lecture 1)

• The simplest mode of communication
• The cell self regulates
• Simple direct mechanism
• They bind to receptors on the outside of the cell
• Internal feedback which will turn off the secretion of the signalling molecules

• Somatostatin - Found in the gut
• It regulates the secetion of HCl.
• HCl is needed for digestion to occur
• Somatostatin is autocrine (self regulation) - Follows a negative feedback loop.
• Somatostatin is produced and secreted by D-cells into the blood plasma side of the D-cell membrane.
• The signalling molecule Somatstain then binds to receptors called SST2R on the same D-cell it was produced from.
• This causes HCl concentrations in the gastic lumen to fall.
• An activation of the somatostatic receptors that are located on the blood plasma side of the d cells which then inhibit AC which causes a reduction of cAMP which switches off the production and secretion of somatostatin. (This is the negative feedback loop.) 

• One cell is regulating an adjacent cell
• The target cell is local - in that it doesnt have to send a signal through the bloodstream or circulatory system
• Paracrine regulation was shown in the last slide via somatostatin going from the D-cell to effect the parietal cell

• Histamine is secreted by enterochromaffin-like cells in the gastric glands.
• This is in resonse to stimulation by acetycholine.
• Histamine binds to H₂ receptors with subsequent activation of adenylyl cyclase
• This igves to an increase cAMP which then promotes the production of proton pumps
• proton pumps facilitates the secretion of HCl
• The release of histamine basically increases the numbers of proton pumps which allows protons (hydrogen ions) to get into the gastic ions which combines with the chloride and creates an incease in HCl

• This type of regulation requires the circulatory system.
• The communication requires the signalling molecules over a comparatively large distance through the body
• This type of communicaton system probably evloved the circulatory system

• An example of endocrine regulation is the hypophyseal portal system. 
• Basically all the blood circulation that occurs in the pituraotry.
• Nervous system control over the endocrine system. 

• Adrenaline can be a hormone and a neurotransmitter, which one depends upon transmission.
• Paracrine = hormone
• Neuronal = neurotransmitter
• Most hormones have effects on multiple targets in the body
• Hormonal duration of action can vary from seconds to days

Hormones are grouped into 4 classes based on their structure:

• Steroids 
• Amine-derived
• Peptides
• Proteins

Steroids = they have a cholesterol backbone and they can cross the plasma membrane as they are hydrophillic

Amine-derived = gererally hydrophillic and are post-synaptic receptors on the outside of the cell

• Synaptic transmission is a very direct type of communication.
• Action potentials active voltage gated calcium channels.
• the influx of calcium causes activation of vesicles. 
• calcium goes into pre synaptic cell and this moves the vesicles towards the synaptic cleft. 
• the release of neurotransmitter at synaptic cleft which then bind to post synaptic receptors
• the communication mechanism isnt going to work unless there is the right post synaptic receptors

Electrical signal is translatted into a chemical signal (release of neurotransmitter) 

In the cholinergic synapse in the brain you have acetycholine receptors and the nicotinic receptors. Both types of receptors your going to get a achange in the polarity. 

Sodium is positively charged going into a cell its going to depolirise. if you have enough release of acteylchline there will be a depolaristion which results in action potentials of the post synaptic neuron.

Metabolsing enzyme choline estarase breaks down the signalling molecules to prevent reoccurance.

A neurotransmitter is a chemical substance released from a neuron and bringing about the transfer of an impulse to another neuron

• it brings about electirucl impuse of a post-synaptic neuron
• Acetycholine and adrenline can also exist as a hormone.
• Adrenaline from acceland glands = hormone
• the reason why some neurotranmitters can be hormones as well is becuase of the mode of communication/transmission. eg adrenaline released from a neuron is a neurotramitter.

Molecular Biology of the Cell, Alberts et al. (6th edition) - Chapter 11, p627-632, Chapter 25, p813-819.