Ion channels and transporters

Question 1

why are active transporters needed?

Answer 1

• they are needed for the flow of ions down the electrochemical gradient to maintain electrochemical equilibrium

Question 2

difference b/w uniport, symport and antiport with examples

Answer 2

1. uniport - transports one substance in one direction e.g. ion channels - Na+, K
2. symport - transports two substances in same direction e.g. co-transporters - Na+/K+/Cl- co-transporter
3. antiport - transport two substances in two different directions e.g. ATPase pumps, ion exchangers

Question 3

give examples of channels, co-transporters, ATPase pumps, ion exchangers

Answer 3

1. channels - Na+,K+,Cl-,Ca2+
2. Co-transporters - Na+/K+/Cl- co-transporter
   K+/Cl- co-transporter
   Na+/neurotransmitter co-transporter (e.g. DAT)
3. ATPase pumps - Na+/K+ pump, Ca2+ pump
4. Ion exchangers - Na+/Ca2+ exchanger, Na+/H+ exchanger

Question 4

what are the characteristics of Na+/K+ ATPase/pump

Answer 4

• Helps maintain electrochemical gradients for Na+ & K+
• 3 Na+ out & 2 K+ in per cycle, electrogenic, BUT <1% I of VGSC so minimal effect on resting Em
• Uses ATP
• 20-40% of brain energy expenditure

Question 5

which neurological disorders are caused by mutations in these Nav channel genes?

1. SCN1A
2. SCN2A
3. SCN3A
4. SCN9A

Answer 5

1. SCN1A - epilepsy, migraine, autism
2. SCN2A - epilepsy, autism, episodic ataxia
3. SCN3A - epilepsy
4. SCN9A - pain in insensitivity and extreme pain disorder

Question 6

which neurological disorders are caused by mutations in these K+ channels?

1. KCNA1
2. KCNQ2,KCNQ3, KCNMA1

Answer 6

1. KCNA1 - episodic ataxia

2. KCNQ2,KCNQ3, KCNMA1 - epilepsy syndrome

Question 7

which neurological disorders are caused by mutations in these Ca2+ channels?

1. CAC1NA1A
2. CACNA1B
3. CACNA1F
4. CACNA1H

Answer 7

1. CAC1NA1A - episodic ataxia, SCA6 and familial hemiplegic migraine
2. CACNA1B - myoclonus dystonia syndrome
3. CACNA1F - X-linked congenital stationary night blindness
4. CACNA1H - childhood absence epilepsy

Question 8

name two inhibitors of Na+/K+ ATPase/pumps

Answer 8

inhibitors

1. cardiac glycosides digoxin (digitalis lanata)
2. ouabain (acokanthera)

Question 9

how do the Na+/K+ in inhibitors cause heart muscle contraction?

Answer 9

• by elevating intracellular Ca2+ (secondary effect via Na+/Ca2+ exchanger)
• Inhibit Na+/K+ ATPase – you dissipate the normal sodium gradient – has an affect on one the antiporters – Na+/Ca2+ exchangers – elevated extracellular Ca+ - increased force of muscle contraction

Question 10

Na+/K+ in inhibitors have neurological & psychiatric side effects
True or False

Answer 10

True