1. Biophysics 702 Patch Clamp Techniques Stuart Mangel, Ph.D.
LEARNING OBJECTIVES
Principles that underlie different electrical recording techniques
Physiological and biophysical information the techniques provide
1. Extracellular recording and multi-electrode arrays
- spiking (all-or-none) information, neural codes conveyed by individual neurons and by groups of neurons
2. Intracellular recording
- measurements of input resistance, synaptic input, and synaptic integration
3. Patch-clamp recording (cell-attached; whole-cell; inside-out patch; outside-out patch)
- measurements of input resistance, synaptic input, synaptic integration; characteristics of voltage-gated ion channels and single ion channel events

2. EXTRACELLULAR VS. INTRACELLULAR RECORDING
Extracellularly and intracellularly recorded voltages are
in the microvolt and millivolt ranges, respectively.

3. Maintaining the resting membrane potential
The Goldman-Hodgkin-Katz (GHK) Equation:
The steady state membrane potential for a given set of ionic concentrations inside and outside the cell and the relative permeability of the membrane to each ion
Vm = ln RT F
pK[K+]o + pNa[Na+]o + pCl[Cl-]i
pK[K+]i + pNa[Na+]i + pCl[Cl-]o
extracellular
intracellular
ENa = +56
Na+ (150)
EK = -102
K+ (3)
ECl = -76
Cl- (120)
ECa = +125
Ca2+ (1.2)
Na+ (18)
K+ (135)
Cl- (7)
Ca2+ (0.1 µM)
Na+,K+-ATPase
-60 to -75 mV
NSCC

4. INTRACELLULAR RECORDING
Measuring EM
Measure the potential difference between two electrodes using a D.C. amplifier
Expected value of the membrane potential is in millivolts (not microvolts), so the gain does not need to be as high

5. Intracellular Recording
When a fine-tipped electrode penetrates the membrane of a cell, one observes a sudden change in the measured potential to a more negative value.
Typical problems
High impedance μE
Damage when cell penetrated

6. MEASURING THE INPUT RESISTANCE
Wheatstone Bridge
Used to measure an unknown resistance
Discovered by Hunter Christie, 1833
Popularized by Charles Wheatstone

7. BALANCING THE BRIDGE R1 = Fixed R R2 = Variable R R3 = Fixed R
R4 = Unknown R ?
To get R2/R1 = R4/R3,
adjust R2, so that there is
no current across B, C
R4 = (R2/R1)·R3

8. CALCULATING THE INPUT RESISTANCE OF A CELL
“Balanced”
“Out of Balance”
Balance the bridge before entering the cell
After impaling the cell,
the bridge is “out of balance” by the R value of the cell
I is known, measure V, and calculate R using Ohm’s Law (V = IR)
R = V/I
Did R increase or decrease?
Did channels open or close?

9. PATCH-CLAMP RECORDING
Neher and Sakmann, Nobel Prize, 1991
Tremendous technical breakthrough that improved the signal to noise ratio of the recording
Record from whole cells or from a small patch of cell membrane, so only a few ion channels (or one) can be studied
High resistance (in giga-ohms) and high mechanical strength of the seal between the glass electrode and the cell membrane enable one to observe very small currents.
The diameter of the tip of patch electrodes can be larger than that of fine-tipped intracellular microelectrodes (1.0 micron vs microns), so that the resistance of patch electrodes is lower (e.g. 5 MΩ vs 200 MΩ). The lower resistance of patch electrodes makes voltage clamping easier.

10. Patch clamp recording configurations
Electrode
Glass pipette
Ion channel
Plasma
membrane
Cell-attached
Whole-cell
Perforated-patch
antibiotics
suction
pull
pull
Inside-out
Outside-out

11. SUMMARY OF ADVANTAGES AND DISADVANTAGES OF PATCH CLAMP CONFIGURATIONS

12. THE VOLTAGE CLAMP

13. THE ACTION POTENTIAL

14. Voltage clamping reveals the ionic currents
that underlie the action potentials observed in squid axons

15. Activation and Inactivation Properties
Ionic Selectivity

16. SODIUM CHANNEL GATING CURRENT

17. Reversal potentials for synaptic currents

18. Inhibitory actions of GABA synapses result from the opening of ion channels selective for Cl-

19. ROLE OF ION TRANSPORTERS IN NEURAL NETWORK FUNCTION
GABA-evoked depolarization
GABA-evoked hyperpolarization
Fig. 1
Fig. 3
Fig. 3. The GABA reversal potential at the starburst amacrine cell (SAC) distal dendrite is more hyperpolarized than at the proximal dendrite due to KCC2 activity. (A, B) GABA was applied onto the proximal dendrite (A) and onto the distal dendrite (B) ~ 100 m from the cell body of a SAC in the presence of cobalt (2 mM) to block synaptic transmission. (C) Average EGABA of the proximal and distal dendrites of SACs were significantly different (p < 0.01). (D) Average EGABA of distal dendrites before and during bath application of FUR (25 M), a selective inhibitor of KCC2 activity, were significantly different (p < 0.01).
Fig. 1. The chloride cotransporters, Na-K-2Cl (NKCC) and K-Cl (KCC2), determine whether the neurotransmitter GABA, which opens Cl- channels, depolarizes or hyperpolarizes neurons, respectively.
Fig. 2
Fig. 2. The dendrites of starburst amacrine cells (green), a type of interneuron in the retina, hyperpolarize to light stimuli that move from the periphery to the cell body (bottom left) and depolarize to light stimuli that move from the cell body to the periphery (bottom right). These directionally-selective responses are generated in part by the differential distribution of the Na-K-2Cl (NKCC) cotransporter (pink) on the cell body and proximal dendrites and the K-Cl (KCC2) cotransporter (blue) on the distal dendrites. The expression patterns of Na-K-2Cl and K-Cl are represented as pink to purple and purple to blue gradients, respectively, on the dendrites and cell body of this starburst cell.
- modified from Gavrikov et al., 2006, PNAS

20. SODIUM CHANNEL CURRENTS RECORDED FROM CELL-ATTACHED PATCH

21. Properties of ACh-gated channels

22. Single open ACh-gated channels behave as simple resistors.

23. Extracellular Mg2+ ions block NMDA channels under physiological conditions.

24. Questions:
Stuart Mangel, Ph.D.
Professor
Department of Neuroscience
The Ohio State University
College of Medicine
Readings:
Kandel, Schwartz & Jessell, Principles of Neural Science – Chaps. 9, 11 & 12
Squire, Berg et al., Fundamental Neuroscience – Chaps. 6 & 11