Lecture Outline03 Zhu

Lecture outline: Bio2000 Fall 2003 Signaling II: Diffusible and electrical signaling factors Michael Xi Zhu, Ph.D. Department of Neuroscience and Center for Molecular Neurobiology The Ohio State University Columbus, OH 43210 614-292-8173 (Phone), 614-292-5379 (Fax), [email protected] A. DIFFUSIBLE MESSENGERS FOR SIGNAL TRANSUDCTION Where are they from? What do they do? Spatial and temporal nature of second messenger signaling. 1. Cyclic nucleotides and sugar nucleosides a) cAMP Formation: Adenylyl cyclase: ATP cAMP + PPi Removal: Phosphodiesterase: cAMP + H2O AMP Targets: Protein kinase A; cAMP-regulated guanine nucleotide exchange factors (GEF); cyclic nucleotide-gated (CNG) channels. b) cGMP Formation:

Receptor guanylyl cyclase Soluble guanylyl cyclase: GTP cGMP + PPi Removal: Phosphodiesterase: cGMP + H2O GMP Targets: Protein kinase G; cGMP-regulated phosphodiesterases; CNG.

c) cADP-ribose Formation: ADP-ribosyl cyclase: Removal: cADP hydrolase: Targets: Ryanodine receptor

β-NAD+

cADP-ribose + nicotinamide

d) NAADP Formation: ADP-ribosyl cyclase: β-NADP+ + nicotinic acid Removal: alkaline phosphatase? Targets: NAADP sensitive Ca2+ stores (NAADP receptor) e) ADP-ribose Formation:

ADP-ribosyltransferase: cADP-ribose hydrolase Removal: ADPR pyrophosphatase: Target: ion channel (TRPM2)

2. Phosphoinositides and derivatives Phosphatidylinositol 4,5-bisphosphate (PIP2) Inositol 1,4,5-trisphosphate (IP3) Diacylglycerol (DAG)

NAD ADPR

NAADP + nicotinamide

ADP-ribose + nicotinamide AMP + ribose 5’-phosphate

Phosphatidylinositol 3,4,5-trisphosphate (PIP3) Formation:

PI cycle Phospholipase C: PIP2 DAG + IP3 PI-3 kinase: PIP2 + ATP PIP3 Removal: DAG: DAG lipase, DAG kinase IP3: IP3 kinases, IP3 phosphatases PIP3: phosphatases PTEN and SHIP Targets:

DAG: IP3: PIP2: PIP3:

protein kinase C; ion channels (e.g. TRPC) IP3 receptor and other IP3 binding proteins ion channels: GIRK, CNG, TRPV1 PDK1-Akt, ion channels?

3. Mental ion (Ca2+) Sources: Internal Ca2+ stores: intracellular Ca2+ channels for Ca2+ release (IP3 receptor, Ryanodine receptor, NAADP receptor). Extracellular space: plasma membrane Ca2+ channels for Ca2+ entry (voltage-gated Ca2+ channel, ligand-gated cation channels, receptor and store-operated channels). 2+ Removal: Ca pumps (PMCA, SERCA) Na+/Ca2+ exchangers Mitochondrial uniporter Targets: Ca2+ binding proteins. There are many of them. Annexins Cl- channel K+ channel PKC Calpain Calmodulin Proteins regulated by calmodulin: Ion channels: NMDA receptor, olfactory CNG channel, Ca2+ channel, K+ channel, Na+ channel, TRP channel Phosphodiesterase Adenylyl cyclase PMCA NO synthase Calcineurin CaM kinase and other kinases 4. Arachidonic acid (AA) and metabolites Formation: DAG lipase: DAG AA + MAG Phospholipase A2: PC AA + LysoPC Removal: Cyclooxygenase (formation of prostaglandins: paracrine, inflammation, pain) Lipoxygenase (formation of leukotrienes: smooth muscle contraction and inflammation) Epoxygenase (formation of epoxyeicosatrienoic acids (EET): potent vasodilators)

Targets:

Dehydrogenase: removes all AA metabolites AA: ion channels (Kv4, ARC) EET: ion channels (SOC, TRPV4)

5. Nitric oxide (NO) Formation: NO synthase: L-arginine L-citrulline Removal: superoxide anions; free radicals. Targets: oxidation and S-nitrosylation of various proteins; soluble guanylyl cyclase. Have roles in smooth muscle contractility, pancreatic secretion, synaptic function, apoptosis B. ELECTRICAL SIGNALING 1. Origin of Resting Membrane Potentials For all living cells, there is a charge difference across the plasma membrane: the inside is more negative than the outside The membrane potential arises from the different ion concentration in the intracellular and extracellular fluids and the selective permeability of the plasma membrane to different ions. Anions: CI- is outside while negatively charged proteins and amino acids are inside. Cations: Na+ is outside while K+ is inside. K+ Diffusion Potential Na+ Diffusion Potential Na+/K+-ATPase 2. Changes in Membrane Potentials due to Ion movement Neurons and muscle cells are able to generate active changes in their membrane potential, which are used to conduct signals. Special ion channels allow cells to change their membrane potentials in response to stimuli. Na+ plays a key role in generating electrical signals in excitable tissues. Opening of an Na+ channel causes the membrane potential to be less negative, i.e. depolarization. This increases the chance of impulse generation. Opening of a K+ channel causes the membrane potential to be more negative, i.e. hyperpolarization. This decreases the chance of impulse transmission. Opening of a Ca2+ channel causes Ca2+ entry into the axon terminus, which in turn triggers exocytosis of neurotransmitter into the synapse. Ca2+ entry also causes membrane depolarization. Opening of a Cl- channel causes the membrane potential to be more negative (hyperpolarization). This decreases the chance of impulse transmission. Opening of a non-selective cation channel generally causes depolarization. 3. Gating mechanisms of ion channels Mechanical gating Chemical gating Voltage gating Second messenger gating 4. Types of electrical signals

Graded potentials: Variable-strength signals that lose strength as they travel through the cell. Action potentials: Signals that travel for long distances through the neuron without losing strength. C. REFERENCES: Molecular Biology of the Cell by Alberts et al., 1994 Fundamental Neuroscience by Zigmond et al., 1999 D. DISCUSSION PAPER Nishiyama M, Hong K, Mikoshiba K, Poo MM, Kato K (2000) Calcium stores regulate the polarity and input specificity of synaptic modification. Nature 408:584-588.