Current clamp

Figure 2.12 From voltage-clamp to current-clamp micro-electrode recordings of synaptic current (/, lower trace) and synaptic potential with superimposed action potential (V, upper trace) from a neuron in an isolated rat superior cervical sympathetic ganglion following a single stimulus (S) applied to the preganglionic nerve trunk. The interval between the stimulus and the postsynaptic response includes the conduction time along the unmyelinated axons of the preganglionic nerve trunk. (SJ Marsh and DA Brown, unpublished)...

Figure 4.5 Influence of oxidant stress on action potentials recorded In an isolated rabbit ventricular myocyte, (a) Control action potential, (b) Action potential recorded 3 min after exposure to oxidant stress induced by the photoactivation of rose bengal (50 nu). (c) Spontaneous and repetitive action potential discharges induced 6.5 min after exposure to rose bengal. Action potentials were recorded via a 2.5 MQ suction electrode and a current-clamp amplifier. The cell was stimulated at 0.1 Hz with a 2 ms suprathreshold current pulse and, when the cell showed automaticity (after 6 min), stimulation was stopped. Redrawn from Matsuura and Shattock (1991b).

The two-micropipette current-clamp technique for examining the massed responses of ion channels on Ascaris body muscle... 

Fig. 21.2. Two-microelectrode current-clamp technique used to observe, in single Ascaris body muscle cells in a body-flap preparation, the response to a controlled pulsed application of levamisole. One micropipette, to measure membrane potential, and another micropipette, to inject current, are inserted inside the area of the muscle cell known as the bag region. Levamisole is applied in a time- and pressure-controlled manner from a microcatheter placed over the bag region of the muscle. A second microcatheter is used to apply additional chemical agents (Martin, 1982).

Fig. 21.3. Two-micropipette current-clamp recording and effect of maintained application of 30 pM levamisole, which produces a 15 mV depolarization (upward movement of trace). The downward transients are the result of injected current pulses used to measure membrane conductance. The trace gets narrower as the input conductance increases from 2.35 pS to 4.35 pS as the levamisole ion channels open. The peak amplitude of the membrane potential response and change in input conductance are used as an assay of the number and activity of the levamisole ion channel receptors present in the muscle cell membrane. The response was fully reversible on washing (not shown).

Avermectin-sensitive sites in A. mum have been identified on pharyngeal muscle (Martin, 1996) using a two-micropipette current-clamp technique (Fig. 21.13A). Glutamate and avermectins produce hyperpolarization and an increase in Cl conductance when either bath-applied or pressure-ejected on to the pharyngeal preparation (Fig. 21.13B,C). These observations establish that one site of action of the avermectins is the pharyngeal muscle of nematodes and that the avermectins can inhibit feeding in nematodes. 

Burdyga Yes. In the guinea-pig ureter application of caffeine (1—2 mM) increases the frequency of Ca2+ sparks and STOCs, and under current-clamp conditions this causes a decrease of the plateau component of the action potential, thus bringing down the Ca2+ and force. In contrast, CPA inhibits Ca2+ sparks and STOCs, and increases the duration of the plateau component of the action potential. This results in an increase in the duration of the Ca2+ transient and amplitude and duration of the phasic contraction. 

Intestinal motility activity. Rat intestinal epithelia mounted in an Ussing chamber attached with voltage/current clamp were used for measuring changes of the short-circuit current across the epithelia. The intestinal epithelia were activated with current raised by serosal administration of forskolin 5 pM. Ethanol extracts of cannabis augmented the current additively when each was added after forskolin. In subsequent experiments, ouabain, and bumetanide... 

Subsequently, serotonin was shown to affect responses to excitatory amino acids in rat neocortical neurons, in cells of the ventrobasal thalamus, dorsal horn neurons, and rat locus coeruleus neurons (Aston-Jones et al. 1991 S. A. Eaton and Salt 1989 Murase et al. 1990 Read et al. 1990 J. N. Reynolds et al. 1988]. Whether the modulatory effect of serotonin is to enhance or attenuate the effect of the excitatory amino acid appears to depend on the brain region investigated. Also, many of the experiments used extracellular recording techniques, although Sizer et al. (1992] used intracellular current clamp in vitro experiments to investigate neurons of the rat entorhinal cortex and neocortex. In the entorhinal cortex and neocortex, the predominant effects of serotonin were to reduce and enhance, respectively, the response to excitatory amino acids. 

The 5-HT1A receptors are coupled to potassium and calcium channels. Intracellular current-clamp recordings in slices containing the DR established that the 5-HT-mediated inhibition involved an increase in potassium conductance, which exhibits inward rectification (18,58). This induced a membrane hyperpolarization leading to a decrease in action potential frequency. Similar responses to 5-HT1A receptor activation have been reported in other neuronal types, such as hippocampal pyramidal cells (16,59) or 5-HT neurons of the caudal raphe nuclei (60). 

Figure 3-3 Original current-clamp recording of a spontaneous beating cardiomyocyte derived from human embryonic stem cells. The cell was superfused with 100 nM E-4031, a potent hERG channel blocker, which lead after an action potential prolongation to early after depolarizations and chaotic electrical behavior at the cellular level (cellular arrhythmia).

Stoelzle S, Haythomthwaite A, Haarmann C et al (2011) Automated patch clamp with current clamp action potential recordings from stem cell derived cardiomyocytes. Biophys J 100(3) 196... 

Spruston The current clamp recordings from the SNS / mice imply that SNS contributes a dramatic amount of current during the rising phase of the action potential, because the amplitude is reduced dramatically. Is that a consistent observation Also, the after-hyperpolarization is much more negative in the SNS mice, implying that there is an actual contribution by SNS during the repolarizing phase of the action potential. 

Under current-clamp conditions, activation of GABA receptors produced an increase in conductance and hyperpolarization of the membrane potential. Under voltage-clamp conditions this was seen as an outward current or influx of negative charge. The reversal potential for the GABA-induced hyperpolarizations was -77+2mV (mean +s.e.m , n = 22). 

Figure 1. Responses of current-clamped, cultured, embryonic cockroach brain neurons to putative neurotransmitters and a neuropeptide. The test compounds were applied by pressure ejection from glass micropipettes onto the soma of the impaled neuron. The membrane resistance was monitored by repeated injection of constant-amplitude current pulses.

Effects of pyrethroid molecules on isolated axons (current-clamp experiments). 

The current clamp experiments of this series show that when the membrane is depolarized by 15 pAf veratridine at room temperature (pH 8.1 about 50 mV), cooling leads to a slow but reversible repolarization (or... 

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