Re: Why do Ethanol, Acetyl choline, Adrenalin affect the heart rate of Daphnia

Hello Calvin,
	Well, I'm going to try and answer your question. Actually, you've come 
across a rather complicated subject. On the surface of the muscle cells 
which make up the heart there are a number of specialized proteins called 
receptors. There are receptors for adrenaline and for acetylcholine. These 
receptors are large proteins which have a part of their structure on the 
outside of the cell (i.e. the part that receives adrenaline or 
acetylcholine) and a part on the inside of the cell (which is involved in 
modulating the contractile force generated by the muscle). When the 
receptor for adrenaline captures a molecule of adrenaline released from a 
nerve or circulating in the bloodstream a number of things happen. The 
binding of adrenaline causes a change in the shape of the receptor such 
that part of the receptor on the inside of the cell is more able to 
stimulate the contraction of the muscle. It does this in a number of ways. 
For example it can stimulate the production of a molecule called cyclic AMP 
which can then activate a number of enzymes which modulate contractility. 
Also, stimulation of adrenergic receptors can directly activate some of the 
proteins found in the cell membrane which are responsible for the 
electrical activity of the cell. In a similar fashion, acetylcholine binds 
to its receptor and essentially causes the opposite response, that is a 
decrease in the contractile force generated by the muscle. Alcohol is a 
different matter entirely. Basically, little is know about the specific 
mechanisms by which alcohol decreases heart rate. Alcohol, of course is a 
general depressant. Some of its metabolites (breakdown products) may 
actually cause the release of adrenaline causing a further complication to 
its effects. I hope this helps.