Chapter 7 notes

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University of Toronto St. George
Cell and Systems Biology
Melanie Woodin

CSB332H1S Ch 7 Reading Pg 113119 120122 127Subtracting K current from total ion current128 lecturerelatedrevealed magnitudetime course of Na currentIonic Basis of the Action PotentialDepolarization rapidly increases Na conductanceSelective Poisons for NaK Channelsgradually increases K conductanceTetrodotoxin TTXpharmalogical equivalent Na activation transient followed by inactivationsaxitoxin STXparticularly useful for inactivating K conductance increase as long as depolarizing pulse Na channelsmaintainedTTXvirulent poison in ovariesother puffer In some cells voltageactivated Ca channels fish organsresponsible for rising phase of act potSTX synthesized by marine dinoflagellatesRepolarization can involve activation of other K concentrated by filterfeeding shellfish ex channel typesbutter clam Saximodusvirulence competes w Act pot can be followed by afterpots periods of TTX clam injection can be fatal whether cooked hyperpolarization or depolarization mediated by or notprolonged changes in membrane conductanceSnail toxinsconotoxinsTTX advantagehigh specificityeliminates Na Resting membrane pot near K eqm pot since high K current after depolarizing voltage steponly permeabilitydelayed K current seenunchanged in amplitudeSquid axonsmajor contributiontime courseVoltage clampnewly developed in 19050s big TTX application to inside of membrane via internal contributionperfusing soln has no effectRisingfalling phases of act pot accompanied by Actions of STX indistinguishable from TTXbind to large transient Na influx then K effluxsame site in outer mouth of Na channelphysically blocksVoltage Clamp ExptsDevised by Cole developed further by Hodgkin Isolation of currents underlying act pot discovery by Huxley Katzblocking voltageactivated K channelsIdentify nature of ionic currents underlying act potSquid axons myelinated frog axons Armstrong determine their magnitudetime courseHillevoltageactivated K currents blocked by Permits us to set membrane pot of cell almost tetraethylammonium TEA in concs10mMinstantaneously to any levelholdclamp it thereleaves Na current intactwhile recording current flowing across
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