Precision constant current sources for
microiontophoresis
During an experiment the resistance of an iontophoresis
pipette may fluctuate for a variety of reasons (mostly biological). This requires
a precision constant current source (or iontophoresis pump as it is popularly
called) which automatically maintains a constant current flow through the
barrel, independently of the electrode resistance. An iontophoresis pump,
in compensation to fluctuations in tip resistance, automatically changes the
voltage applied to the iontophoresis pipette. Microiontophoresis pumps come
in two basic varieties:
- (1) Pumps which deliver currents in the 1-10 microampere range for extracellular
deposition of dyes and tracers
and
- (2) Pumps which deliver currents in the nanoampere range for intracellular
dye or tracer deposition or to determine the effects of extracellularly
applied substances upon firing parameters of neurons. In the latter case,
extremely small amounts of neuroactive
substances (transmitters, modulators, hormones, drugs) ejected into
the near vicinity of neurons to study the pharmacological responses of single
nerve cells.
Our BAB-501 iontophoresis pump was designed specifically
for iontophoretic deposition of neural dyes and transport tracer substances
such as Pontamine Sky Blue, Horseradish peroxidase (HRP) or Phaseolus vulgaris
leucoagglutinin. It provides constant currents up to 20 microampere with either
polarity, its maximum compliance voltage is 500 V.
The Union-40 iontophoresis pump is for intracellular
deposition of tracer substances as well as for extracellular ejection of neuroactive
substances to test their effects on cell firing. It is capable of driving
100 nanoampere current through pipettes having resistance as high as 400 MegOhm.
The BAB-501 microampere iontophoresis pump for
extracellular tracer deposition
Back panel view
The maximum output current is 20 microampere set by a ten-turn
("Current") dial with an accuracy of 0.01 microampere. Three modes
of operation can be selected. In continuous mode, iontophoresis current is
continuously generated when the polarity switch is in "Positive"
or "Negative" position. In external mode, the BAB-501 can be gated
through its "Ext.In" BNC jack by any logic pulse generator or computer.
The output current is on whenever the gating input is logic high, off when
it is logic low. In pulse mode, an internal timer turns on the output current
for 7 s in every 14 s generating 7 s on/7 s off cycles. Polarity of the output
current is switch selected. A built-in 10 Mohm resistor can be selected for
termination to preset required current. The current sensing resistor is in
series with the current source providing a true measurement of the output
current. Please, find the BAB-501 manual here.
Specifications
| Output current range: |
0±20 microampere |
| Compliance voltage: |
±500 V, maximum |
| Polarity: |
+/Off/-, switch selectable |
| Termination: |
Electrode (micropipette) or 10 MOhm internal dummy load |
| Load configuration: |
Floating |
| Mode of operation: |
Continuous/Externally timed/Pulsed (internal timer) |
| External timing: |
Through Input BNC jack. Optical isolation |
| Pulse duration: |
5 seconds, factory set |
| Duty cycle: |
50% (7 s on/7 s off) |
| Dimensions: |
6.67" x 2.19" x 6.45" (169.5 x 55.6 x 164 mm) (WxHxD) |
| Weight: |
1.7 lb (770 grams) |
| Power source: |
12 V DC external power supply, purchase
separately |
To place an order see Kation Scientific's Order
and Price list page.
The Union-40 nanoampere iontophoresis pump for
intra- and extracellular studies
Back panel view
This model is an upgraded version of our previous Union-36
iontophoresis pump. This precision constant current source may be operated
in two switch-selectable current ranges. The 0-20 nA range is for intracellular
dye or tracer deposition. The 0-200 nA range permits extracellular delivery of
various substances to test their effects on neuronal firing. The retention and
ejection currents can be set by the respective front panel knobs with an accuracy
of 0.1 nA. Switching between the retention and ejection currents can be done
manually using the 'Mode' selector switch or can be automated through the back
panel 'Remote' BNC jack using a computer or timer. The ejection current is activated
whenever the remote input is logic high, retention current is on when it is logic low.
The polarity of the ejection current is switch selected, while the polarity of the
retention current is automatically set. The current sensing resistor is in series
with the current source providing a true measurement of the output current. The
output current can be monitored by computer or chart recorder using the back panel
'I monitor' BNC jack. Requires an external 12 VDC power supply. Shipped complete
with user guide. Please, find the Union-40 manual here
Specifications
| Ejection current range: |
0- ±200 nA or 0- ±20 nA, switch selectable |
| Retention current range: |
0- ±20 nA or 0- ±2 nA |
| Compliance voltage: |
±40 V, maximum |
| Max. pipette impedance: |
400 MegOhm at 100 nA output, 200 MegOhm at 200 nA output. |
| Load configuration: |
Floating |
| Mode of operation: |
Manual 'Retain' or 'Eject' by toggle switch, 'Remote' by external timer or computer |
| Remote control: |
Through back panel 'Remote' BNC jack by TTL or CMOS signals. Optical
isolation is up to 5000 V. |
| Current monitor: |
Through back panel 'I Monitor' BNC jack; 10 mV/nA |
| Dimensions: |
6.67" x 2.19" x 6.45" (169.5 x 55.6 x 164 mm) (WxHxD) |
| Weight: |
1.7 lbs (770 grams) |
| Power source: |
12 V DC external power supply, purchase
separately |
| Power consumption: |
350 mA, maximum |
To place an order see Kation Scientific's Order
and Price list page.
References:
Conn, P.M., ed. (1991) Electrophysiology and microinjection. Methods
in Neurosciences, Vol. 4., Academic Press: San Diego.
Dreyer, F. and K. Peper (1974) Iontophoretic application of acetylcholine:
advantages of high resistance micropipettes in connection with an electronic
current pump. Pflügers Archive, 348: p. 263-272.
Geller, H.M. and D.J. Woodward (1972) An improved constant current
source for microiontophoretic drug application studies. Electroencephalography
and Clinical Neurophysiology, 33: p. 430-432.
Gerhardt, G.A. and M.R. Palmer (1987) Characterization of the Techniques
of Pressure Ejection and Microiontophoresis Using In-Vivo Electrochemistry.
Journal of Neuroscience Methods, 22(2): p. 147-160.
Gottschaldt, K.M., T.P. Hicks, and C. Vahle-Hinz (1988) A combined
recording and microiontophoresis technique for input-output analysis of single
neurons in the mammalian CNS. Journal of Neuroscience Methods, 23(3): p. 233-240.
Park, M.R. (1989) Constant current source for iontophoresis. Journal
of Neuroscience Methods, 1989. 29: p. 85-89.
Purves, R.D. (1981) Microelectrode methods for intracellular recording
and iontophoresis. New York: Academic Press.
Stamford, J.A., ed. (1992) Monitoring neuronal activity: a practical
approach. 1992, Oxford University Press: Oxford.
Walker, T., N. Dillman, and M.L. Weiss (1995) A constant current
source for extracellular microiontophoresis. Journal of Neuroscience Methods,
63(1-2): p. 127-136.
Yu, D. and F.J. Gordon (1994) A simple method to improve the reliability
of iontophoretic administration of tracer substances. Journal of Neuroscience
Methods, 1994. 52(2): p. 161-164.
