[HAPS-L] "I'm going to pick a fight"

Okay. Would someone please explain to me the rationale behind referring to calcium as the second messenger in the IP3/DAG second messenger system, rather than IP3 and DAG. In the cAMP system, cAMP is the molecule made that then activates a cascade of events and is thus termed the second messenger. In almost all of the texts that I have seen (including Guyton’s 11^th ed.) the second messenger is said to be “Calcium”. The only text that seems to get it right is Berne, Levy, Koeppen, and Stanton’s 5^th ed. Wherin it is stated that there are THREE systems. The cAMP system (with cAMP as the second messenger), the Calcium-Calmodulin system (with Calcium as the second messenger), and the Membrane Phospolipid system in which IP3 and DAG are the second messengers. Other second messengers are listed (e.g. cGMP, NO, etc.), but in an Intro to Physiology course we tend to focus only on the two main pathways (cAMP, IP3/DAG). I have always argued that the second messengers in the IP3/DAG system are IP3 and DAG. These are the molecules synthesized by the enzyme activated by the G-protein. I thus tell my students to ignore what the text says (Fox in my case) and refer to IP3 and DAG as the second messengers. It becomes very confusing to my students when they see the cAMP path in their textbook as:

Receptor à G-Protein à Enzyme à Second Messenger à Cellular Cascade

While the IP3/DAG system is thus:

Receptor à G-Protein à Enzyme à Intermediate Molecule?? à Cellular Effect à Second Messenger à Cellular Cascade.

Seems to me that the only textbook that has attempted to clear up this confusion is the Berne book. Anyone want to explain the rationale behind this confusing bit of nomenclature??

Dayton J. Ford, Ph.D.

Associate Professor of Biological Sciences

St. Louis College of Pharmacy

4588 Parkview Place

St. Louis, MO 63110

dford@xxxxxxxxxx

314-446-8463 voice

314-446-8460 FAX

[HAPS-L] "I'm going to pick a fight" - Braveheart