Lecture 7

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Cell and Systems Biology
Melanie Woodin

CSB332H1S L7 Jan 30 2012Conductanceslope of iv curveNot absolute conductance use curve to look at how conductance depends upon membrane potPlotting current amplitude against membrane pot on x axisSlopeless at 100 and 50 mV holding pot than at morevaluesLarge conductance at lower curve where slope shallow just changes small amt w change in membrane potSlope shows how much conductance depends on membrane potEx at 3 conductance small small current but conductance still greatly depends on membrane pot ex from 2 to 25Ex Katzhad to make every tool used in expts designBetter technology todayx examine ionconcs using fluorescence indicatorstaggedRecord concs of particular ionFirst developedCa sensors load indiv neurons or tissue w ca indicator use microscope for fluorescence to visualize when stimulated what Ca is actually doingCan quantify Ca increase and what absolute values are50 yrs agoPresynaptic terminal of squid giant axonA predominantly blue at bottom 3315987 micromolars of orexin CaPeakssome local increases in Ca but overall very blueIllustrating where synaptic delay comes fromB given train of act pots to presynaptic What we require to induce neurotransmitter releaseterminalspeaks of terminals now redCa releaseVery standard on continual basisDelay larger btwn 25ms on avg larger than could Now being use to record membrane pots in cells be from diffusion aloneinstead of using electrodes using voltagesensitive Synaptic delay when start presynaptic dyes being developed use Cl senstivie indicator depolarization to when measure it at postsynaptic but technical challaenges recording Cl currents terminal largely from time to open voltage gated ca moving in right direction but need microscope w channels have ca flow in and lead to special fluorescence capabilities thata re very neurotransmitter releasecomplexRed Injecting current to mimic presynaptic act potAdvantage of indicatorssimplify process can use Shows voltage channels alone can elicit the more simple microscopeblack ca currentShows delay btwn presynaptic depolarization Nanodomains local ca increase thru 1 voltagegated and ca currentneed before can record ca chennalca grad large enough to activate ca postsynaptic responsesensor for vesicle releaseA1 peak w red assume Postsynaptically transmitters have to bind to open 1 nanodomainmore ion channelsMicrodomains ca influx thru voltagegated ca channels in active zone at same timeCa flows into microdomain in active zonetransmitter release
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