L3 - ion selectivity and permeability Flashcards
what region of a channel determines selectivity and permeability?
- pore region
what is selectivity and how is it determined?
- how easily an ion enters a pore
- determined by Vrev
what is permeability and how is it determined?
permeability is how easily an ion moves through a pore (through pore and out the other side)
determined by current magnitude
what is Vrev?
the reverse potential - the potential where there is no net movement of charge = I=0
how is Vrev determined?
determined by relative selectivity
what calculation shows Vrev?
goldman equation determines reversal potential
what is the value used which is temperature dependent in the goldman equation?
61 if mammalian body temperature (37 degrees)
58.2 if room temperature
how do you calculate relative selectivity?
- calculate Vrev of solution A
- calculate Vrev of solution B (usually sub one ion for another)
(calculated using goldman equation)
- then calculate the shift in Vrev
- follow calculation steps
what determines relative selectivity molecularly?
- key aa’s line the pore and are different aa’s for different channels
- is a common sequence for channels
what is the signature sequence which determines selectivity in potassium channels?
TXXTXGYG
- sequence conserved/found in all K channels. Consists of 8 amino acids with 1,5,6 and 8 being most important in potassium ion selectivity
which aa’s in TXXTXGYG are important and how was this determined?
aa. 1,5,6,8 (no longer potassium selective when these aa’s are mutated)-e.g. let more Na+through
- aa’s were mutated and selectivity was examined in ooctyes
- NH2 was removed (removed ball and chain so can activate but cant inactivate)
what regions are important in Na+ selectivity?
D1-D4 - mutations were made to cysteine (400, 755,1237,1529
- D1,D2 mutations - decrease in Na+ - less selective for sodium
- D3,D4 mutations - turn sodium channels into calcium selective channels
