Presentation is loading. Please wait.

Presentation is loading. Please wait.

Recording membrane voltage in current-clamp mode from Carbone, Cicirata, Aicardi, EdiSES, 1° ed. (2009)  Recording resting potentials, neuronal firings.

Similar presentations


Presentation on theme: "Recording membrane voltage in current-clamp mode from Carbone, Cicirata, Aicardi, EdiSES, 1° ed. (2009)  Recording resting potentials, neuronal firings."— Presentation transcript:

1 Recording membrane voltage in current-clamp mode from Carbone, Cicirata, Aicardi, EdiSES, 1° ed. (2009)  Recording resting potentials, neuronal firings (trains of APs), pacemaker activities, graduate potentials requires glass microelectrodes of high resistance ( M  )  The cell can also be hyperpolarized or depolarized to regulate the resting and to evoke APs by passing a constant or stepwise membrane current. The current electrode is usually low-ohmic (k  -M  ) and does not necessarily penetrate the cell.  Measuring voltages and passing currents can be done with the same microelectrode How?

2 It can be used to make sums, subtractions, integrals, derivatives or any other mathematical operation of the input signals Recording membrane potentials with operational amplifiers What is an operational amplifier? Is a solid-state amplifier with the following characteristics: With open circuit: high gain (A) = ∞ (≈ 2x10 5 ) high R in = ∞ (≈ 1x10 14  ) low R out = 0 (≈ 10  )

3 1 st example - The voltage inverter Due to the high gain of the op. amplif., the blue point acts as a “virtual ground”. There is no current flowing behind:  = 0 and i a =0 (V i -  ) (  -V o ) R1R1 = + i a R2R2 At the blue junction: i 1 = i 2 + i a ViVi VoVo R1R1 = - R2R2 VoVo R2R2 ViVi R1R1 (inverting) The gain is A = - R2R2 R1R1 R in = R 1 R out = 0 

4 2 nd example - The non-inverter but i = ViVi R2R2 (V o - V i ) = R 1 i Assuming i a = 0 and  = 0: (non-inverting) The gain is A = 1 + R1R1 R2R2 R in = ∞  R out = 0  V o = V i + R 1 ViVi R2R2 thus V o = 1 + V i R1R1 R2R2

5 3 rd example - The unity-gain, buffer amplifier (the “voltage-follower”) It has the same configuration of the previous case except that: R 2 = ∞ and R 1 = 0 V o = 1 + V i R1R1 R2R2 The previous equation: becomes: VoVo ViVi = 1 It is the ideal “buffer amplifier” for coupling high-resistance microelectrodes (>100 M  ) with instruments which measure the voltage (oscilloscopes, computer interfaces, ….) The gain is A = +1 (unity) R in = ∞  R out = 0 

6 A single-electrode current-clamp amplifier

7 Current-clamp and voltage-clamp recordings for complete electrophysiological analysis  Under these conditions, the Ohm law: V m = R m I m can be simplified to: K = R m I m I m = I m  g m K RmRm  Action potential recordings in current-clamp (I m = 0) is optimal for recording neuronal activity without perturbing the cell  Data interpretation in terms of voltage-gated ion channels, however, is difficult since membrane voltage changes continuously with time  A good compromise is “clamping” the voltage to a fixed value and measure the current (V m = K)

8 from Carbone, Cicirata, Aicardi, EdiSES (2009) The voltage-clamp circuit (Cole & Curtis, 1948)

9 The patch-clamp technique Neher & Sakmann (1981)

10 Na + and K + currents at fixed voltages (Hodgkin & Huxley, 1952)

11 Physiological and pharmacological separation of Na + and K + currents

12 The voltage dependence of Na + and K + conductances To calculate the Na + and K + conductances we use the following equations: I Na = g Na (V m – E Na ) I K = g K (V m – E K ) with E Na = +63 mV with E K = -102 mV

13 The voltage dependence of Na + and K + conductances

14 Tetrodotoxin (TTX): the classical Na + channel blocker A pufferfish containing TTX

15 The  -conotoxin GVIA: the N-type Ca 2+ channel blocker The conus geographus from Philippines

16 Noxiustoxin (NTX): a blocker of voltage-gated K + channels Centruroides noxius (female from St. Rosa, México)

17 The voltage-gated Na +, K + and Ca 2+ channels

18 Suggested readings: General: Chapters 1-3 in Purves et al. Neuroscience, Sinauer, 4° ed. Chapters 1-3 in Carbone et al. Fisiologia: dalle molecole ai sistemi integrati, EdiSES, 1 st ed. Technical: The axon guide: A Guide to Electrophysiology & Biophysics Laboratory Techniques Down-load from:


Download ppt "Recording membrane voltage in current-clamp mode from Carbone, Cicirata, Aicardi, EdiSES, 1° ed. (2009)  Recording resting potentials, neuronal firings."

Similar presentations


Ads by Google