Informational meeting for Beta Beta Beta (TriBeta), the National Biological Honor Society When & Where? At 6:00 pm in 215 Coker on Thursday, September 15 Why? Connect with other biology students Connect with the department Learn about career planning, undergrad research, volunteering, and other exciting stuff SEEfor more infowww.unctribeta.org Undergraduate Research at Carolina Biol 98 Genetics Approach Cell Surface Receptors Signal Transduction Nerve Cells !! Electrical- intracellular Chemical- intercellular Sensory, motor, interneurons Last time, we focused on transporters and pumps. Now, lets understand how channels selectively transport ions and do work. The goal is to integrate this understanding into workings of nerve cells. (Facilitated diffusion) You already read about bacteriorhodopsin, Pores are the simplest form (know: gap junctions and porin) But channels are more than that. Because ion channels are selective and can be gated. The typical ion channel fluctuates between closed and open conformations. A million ions per second!!! A thousand times faster than carriers. BUT, only down electrochemical gradient. Ion flow alters the voltage potential. It is this membrane potential that underlies all electrical activity of the cell, plant, fungi, animal. Membrane potential is extremely important- We need to be able to measure it in real time. also whole cell Its possible to actually measure the conformational changes of a single protein. Channel current max, multiples of this for more than one. Note, that channels flicker, even when constantly stimulated, like here. So then, how can it be regulated? Answer: its a probability thing. Note : PICO amps i.e !! Note: MILLIseconds Note: either fully open or fully closed. What types of stimuli are able to regulate the probability of channel opening? Gated ion channels respond to different types of stimuli. Different ions, Different set V Many different ligands Meaning touch. Membrane potential is established by imbalance of electrical charge across the membrane- its like a capacitor. Cells have lots of organic acids balanced largely by potassium. Potassium is high inside. Intracellular ion environments and membrane potential The distribution of ions on both sides of the impermeable barrier is set like the cell and blood. No ion flow possible so V=0 Now, open a Na+ selective channel Na+ move left until positive charges build on the left and negative charges on right V= -59 mV with respect to the right (out) Now, open a K+ selective channel Same except V= -59mV with respect to the cytoplasm. The movement of ions and the membrane potential can be predicted by simply knowing the concentration difference across the membrane. The Nernst equation: V= 62log 10 (Co/Ci) Dont memorize it but understand it. Where do hippopotamuses study? At the hippocampus Hippocampal interneurons make about 1000 synapses. Anti-MAP2 green, dendrites Antisynaptogenin- orange, synapes !!!!!!!!!!!! 100 meters per second!!!!!!!!!!!! Stimulus is +20 mV Bang! action potential The behavior of the membrane without a threshold. A voltage-gated sodium channel has three stable conformations The excited but inactivated state is key to propagation. Behavior at a single position along an axon. Opening and closing of ion channels cause predictable changes in membrane potential. 1.Opening Na + causes depolarization 2.Opening K + causes hyperpolarization** 3.Opening of nonspecific channels cause depolarization 4.Opening Cl - channels causes hyperpolarization 5.At resting potentials, voltage-gated channels are closed. 6.Local perturbation open Na+ channels, local depolarization 7.** Delayed potassium channels open a few millisec. after Electrical signal is converted to chemical signals at the synapse. Chemical signals at the postsynapic cell is converted by to electrical. Like GABA Prozac blocks reuptake of excitatory, serotonin Valium enhances GABA Curare blocks the acetylcholine receptor Strychnine is antagonist for the GABA receptor Dendrites are green Axons are red Large-diameter neurons can propagate a potential father and faster Even still, the distance is short- 0.1 5 mm. But axon lengths can be meters. Movement is saltatory, jumpy due to myelin sheath. Myelin increases speed fold 100 m/s Actually, very few ions are moving, thus action potentials continue for awhile in the absence of ATP (+DNP) Glial cells= Schwann cells in peripheral vs. oligodendrocytes in CNS A high density of Na+ channels tethered by ankrin