Prob Set 5 Q&A - Problem Set 5 Cellular...

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1 Problem Set 5 Cellular Neurobiology Fall 2010 1. Calcium is an important second messenger used in a variety of intracellular pathways. a. What are the 4 methods a cell uses to increase intracellular levels of Ca? How do each of these methods work? 1) Voltage Gated Calcium channel Calcium channel opens in response to a depolarizing voltage above threshold causing Ca influx due to the large concentration gradient across the membrane. 2) Ligand-Gated Ca permeable channel Channel (which is permeable to Ca) opens in response to a ligand attachment causing a Ca influx similar to a voltage-gated channel. 3) Ryanadine Receptor: activates in response to a rise in intracellular calcium levels. This causes Ca efflux from the intracellular Ca stores. 4) IP3 Activated by upstream 2 nd messanger pathway and leads to an efflux of Ca from intracellular Ca stores. b. What are the 4 methods a cell uses to remove calcium from the cytoplasm? How do these methods work? 1) Na/Ca exchanger A channel that exchanges Na for Ca thereby expelling Ca from the cytoplasm. 2) Membrane Ca pump Calcium pump that uses ATP to actively pump Ca ions into the extracellular space. 3) Ca Binding proteins Bind Ca and remove their activating ability (acts as a Ca buffer). 4) Intracellular Ca pump uses ATP to ump Ca in the cytoplasm back into the intracellular Ca stores. 5) Mitochondria absorb calcium. 2. Dendritic spines act as “Ca bottles”, largely confining the entering Ca to the spine interior. However, charge transfer generated by ions entering through the postsynaptic ligand-gated ion channels transfer very quickly from the spine into the dendritic shaft to add with currents from other spines. What accounts for the apparent discrepancy in outcomes? The spine neck restricts diffusion, thereby causing most of the calcium to remain in the spine head until it is either bound or extruded. Charge transfer resulting from ion movement across the plasma membrane, however, is very quickly transmitted along the
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