Calcium Is a Second Messenger in Many Signal Transductions

In many cells that respond to extracellular signals, Ca2 + serves as a second messenger that triggers intracellu-lar responses, such as exocytosis in neurons and endocrine cells, contraction in muscle, and cytoskeletal rearrangement during amoeboid movement. Normally, cytosolic [Ca2+] is kept very low (<10~7 m) by the action of Ca2+ pumps in the ER, mitochondria, and plasma membrane. Hormonal, neural, or other stimuli cause either an influx of Ca2+ into the cell through specific

Hormone (H) binds to a specific receptor.

Extracellular space

Phospholipase C (PLC)

Plasma membrane

Extracellular space

Phospholipase C (PLC)

Plasma membrane

FIGURE 12-19 Hormone-activated phospholipase C and IP3.Two intracellular second messengers are produced in the hormone-sensitive phosphatidylinositol system: inositol 1,4,5-trisphosphate (IP3) and diacylglycerol. Both contribute to the activation of protein kinase C. By raising cytosolic [Ca2+], IP3 also activates other Ca2+-dependent enzymes; thus Ca2+ also acts as a second messenger.

TABLE 12-5 Some Signals That Act through Phospholipase C and IP3

Acetylcholine [muscarinic MJ

Gastrin-releasing peptide

Platelet-derived growth factor (PDGF)

^-Adrenergic agonists

Glutamate

Serotonin [5-HT-1c]*

Angiogenin

Gonadotropin-releasing hormone (GRH)

Thyrotropin-releasing hormone (TRH)

Angiotensin II

Histamine [HJ*

Vasopressin

ATP [P2x and P2y]*

Light (Drosophila)

4 Steps To Permanent Weight Loss

4 Steps To Permanent Weight Loss

I can't believe I'm actually writing the book that is going to help you achieve the level of health and fitness that you always dreamed of. Me, little scrawny sickly Darlene that was always last picked in gym class. There's power in a good story here so get this book now.

Get My Free Ebook


Post a comment