capacitance Capacitance C unit F Faraday t time

capacitance Capacitance (C) unit = F (Faraday)

t : time constant

Ex) Resting membrane potential

[Chapter 2] Classical Biophysics of the Squid Giant Axon Action potential in nerve membrane → Electrically excitable • • <History> 1902 • Bernstein's 'Membrane Hypothesis' : The existence of a cell membrane 1905 • 'Self -stimulatory' Hermann : propagation in axons

• Keneth S. Cole : membrane is a RC-circuit • Hermann (1905) : Cable theory: electrical disturbance in a local circuit → spread passively to neighboring segment • 1935 A. L. Hodgkin: depolarization spreads passively ∴ A. P. propagate eletrically • 1936 Young: discovery of squid giant axon • 1939 Cole & Curtis: measurement of membrane conductance

• Hodgkin & Huxley, 1939; Curtis & Cole, 1940 • An intracellular micropipette in squid giant axon → measurement of a full action potential • Overshoot: Potential is higher than 0 m. V; ⇒ Due to Na+ • 1949 Hodgkin & Katz : Na+ hypothesis; Replacement of Na+ with choline or glucose

Voltage clamp technique (1949) • (Marmont, Cole, Hodgkin, Huxley & Katz) • → voltage clamp : control the membrane potential • cf. membrane → excitable ∴ membrane potential is not stable! ∴ To stabilize membrane potential → using voltage-clamp ⇒ This technique revolutionize the Biophysical areas.

Voltage clamp technique • 세포의 크기가 작아야 보정해주는 current가 골고루 갈 수 있다. ∴ current를 측정하면 feedback Amp가 set voltage와 실제 unstable membrane voltage와의 difference를 전하의 input과 output을 통하여 보정해 준다. ◎ Advantage of using voltage-clamp technique ① 'hold' the membrane potential at the interested voltage ② To record membrane current

Voltage clamp in squid giant axon • 1949 axial wire : To space-clamp squid giant axon은 커서 Axon 자체에 wire를 꽃아 넣는다 • Electrode 2개 필요 : recording용, 보정용 • 비교적 작은 cell에서 고루 분포하여 조절 가능, .

1) Whole cell (단, cell이 작은 경우) 2) Xenopus oocyte는 크기가 크기 때문 에 두 개의 electrode가 필요함 3) Single channel recording (=patch clamp)

Separation of INa & Ik

◎ Separation of INa & IK : Hodgkin & Huxley ⇒ Ionic conductance (g : conductance of ion) I = g*E • RC-Circuit of membrane (Fig 2 -10) gion : Time and voltage dependent!

Na+ channel opens quickly and closes quickly. K+ channel opens slowly! So, g. Na & g. K are time dependent!!

※ Measurement of Inactivation : 2 pulse protocol • Pre-pulse (or conditioning pulse) • Test-pulse : to measure un-inactivated current ⇒deactivated

◎ : 2 kinetic processes (activation & inactivation) ① activation : • rapid, • voltage-dependent (fig 2 -13) ② Inactivation : slow process that closes during depolarization • Once inactivated, membrane should be hyperpolarized to remove the inactivation (deactivation) • Inactivation of Na+ ch → loss of excitability ① refractory period of excitable tissues ② loss of excitability due to anoxia or metabolic block (Fig 2 -15) Recovery from Sodium Inactivation