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PubMed1995

The effect of the single aortic cross-clamp technique on cardiac and cerebral complications during coronary bypass surgery.

Cardiac and cerebral events during coronary artery bypass graft (CABG) surgery remain a major cause of morbidity and mortality. Efforts made to reduce these events will have a significant impact on CABG results. The objective of this study was to examine our results in 394 patients undergoing primary CABG using the single clamp technique that probably has better myocardial and cerebral protective properties than the conventional technique of partial aortic occlusion. Age range was 35 to 88, mean of 66 years, and 168 (43%) were > or = 70 years of age; 121 (31%) were females, 118 (30%) were diabetic, 339 (82%) were in New York Heart Association Functional Class III or IV, 77 (20%) had a preoperative intra-aortic balloon pump, 213 (54%) were nonelective, 293 (75%) had three vessel disease, and 55 (14%) had critical left main coronary artery stenosis. Antegrade crystalloid cardioplegia was used in the majority of patients, and the distal and proximal anastomoses were sequentially constructed during a single period of total aortic occlusion. The mean number of grafts was 3.5, and 339 (86%) had > or = 3 grafts; at least one internal mammary artery was used in 346 (88%), a sequential vein or mammary artery in 181 (46%), and 55 (14%) had at least one coronary endarterectomy. The mean cross-clamp time, bypass time, and time to wean off bypass were 63, 83, and 20 minutes, respectively. The overall operative mortality was 11 of 394 (2.8%), a myocardial infarction/low-cardiac output state occurred in 19 (4.8%), and a stroke in 3 (0.8%).(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1989

Membrane actions of ethanol on rabbit sino-atrial node studied by voltage clamp method.

Electrophysiological effects of ethanol on rabbit sino-atrial node were studied by means of the double-microelectrode voltage clamp method. In spontaneously beating preparations, ethanol (above 1%) decreased the maximum rate of depolarization of the action potential. Furthermore, 3% ethanol produced a significant decrease in the action potential amplitude, the action potential duration at 50% repolarization and the rate of the diastolic depolarization. Of the current systems, voltage clamp studies showed that ethanol reduced the slow inward current, the time-dependent potassium outward current and the hyperpolarization activated inward current. These observations indicate that ethanol does not have an effect on a single current system, but directly modifies the spontaneous discharge of sino-atrial node pacemaker cells due to a reduction of the time-dependent current systems.

Action Potentials↗
PubMed1986

Saliva and sweat secretion in man during a one-hour calcium clamp.

The effect of a 1-h calcium infusion, directly regulated to obtain and maintain a predetermined blood calcium level ('calcium clamp'), on the composition of parotid saliva, mixed saliva, and sweat was determined in healthy volunteers. An increase in amylase content of the parotid saliva under hypercalcaemic conditions was observed, but the 'calcium clamp' had no effect on flow rate, total and ionized calcium, sodium, potassium, and phosphate levels as well as pH in parotid and mixed saliva. The sweat calcium concentration was negatively correlated with sweat rate, in contrast to sodium and chloride concentrations. Increasing serum calcium levels did not affect ionic composition of the sweat and sweat flow rate.

Adult↗
PubMed1989

Action potentials of cultured human oat cells: whole-cell measurements with the patch-clamp technique.

Oat cells (of the small cell carcinoma of the lung) have been reported to generate calcium action potentials. The calcium channels have further been suggested to play a crucial role in the relation between oat cell carcinoma and the often associated myasthenic syndrome. We have examined cultured human oat cells (U-1690) under voltage-clamp conditions, using the patch-clamp technique. We found, contrary to previous reports, that the action potential was caused by sodium and potassium currents. No calcium current was detected under these conditions, which indicates that calcium channels, if present, are very rare. The findings restrict, but do not rule out, the hypothesis that calcium plays a key role in the carcinoma/myasthenic syndrome relation.

Action Potentials↗
PubMed1989

Application of a new technique--blood pressure clamping--for analysis of prostaglandin interference with sympathetic neurotransmission in man.

To circumvent baroreceptor reflexes following drug-induced interference sympathetic neurotransmission, a new technique - blood pressure clamping--has developed. This implies that the sympathetic activity in an awake human is 'clamped' at a supranormal level by infusion of a vasodilator. In 11 healthy volunteers nitroprusside or saline was randomly infused in two consecutive 2-h periods. Plasma and urinary catecholamine levels were analysed by liquid chromatography. The experiments were repeated after random administration of the prostaglandin synthesis inhibitor, ibuprofen, or placebo. In the basal state (no ibuprofen, saline infusion) the mean arterial blood pressure was 81.4 +/- 2.3 mmHg, the heart rate was 60.9 +/- 0.3 beats min-1 and the plasma level of noradrenaline was 1.12 +/- 0.15 nM. Infusion of nitroprusside at a dose lowering the mean blood pressure by 11.6 +/- 1.6 mmHg and increasing the heart rate to 74.6 +/- 2.9 beats min-1 elevated plasma noradrenaline to 2.86 +/- 0.39 nM. After pretreatment with ibuprofen (saline infusion), the systemic blood pressure, the heart rate, and the plasma and urinary levels of noradrenaline were unaffected in comparison to before drug (80.1 +/- 2.3 mmHg, 58.4 +/- 0.3 beats min-1 and 1.13 +/- 0.12 nM respectively). Infusion of nitroprusside at a rate lowering the blood pressure by 11.2 +/- 2.4 mmHg and increasing the heart rate to 74.4 +/- 0.5 beats min-1, elevated the plasma level of noradrenaline to 2.46 +/- 0.38 ng ml-1, which is not different from before ibuprofen. The amount of nitroprusside required to lower the blood pressure was not different in the presence and absence of ibuprofen.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1989

Patch clamp techniques used for studying synaptic transmission in slices of mammalian brain.

Procedures are described for recording postsynaptic currents from neurones in slices of rat brain using patch clamp techniques. The method involves cutting brain slices (120-300 microns thick) with a vibrating microtome followed by localization of cell somata, which can be clearly seen with Nomarski differential interference contrast optics in the light microscope. Tissue covering the identified cell is then removed mechanically and standard patch clamp techniques are applied. Using these methods, spontaneously occurring and stimulus-evoked inhibitory postsynaptic currents (IPSCs) were recorded from neurons in rat hippocampus at greatly improved resolution. In the presence of tetrodotoxin, to block presynaptic action potentials, spontaneous IPSCs seldom exceeded 25 pA. Evoked IPSCs elicited by constant electrical stimulation of a presynaptic neurone were larger and fluctuated in their amplitudes. Single-channel currents, activated by the putative inhibitory transmitter gamma-aminobutyric acid (GABA), had a size of about 1 pA. The number of postsynaptic channels activated by a packet of inhibitory transmitter is probably not more than thirty, nearly two orders of magnitude smaller than previously reported estimates for CNS synapses. This might reflect matching of synaptic efficacy to the high input resistance of hippocampal neurones and could be a requirement for fine tuning of inhibition.

Animals↗
PubMed1970

Time course of the sodium influx in squid giant axon during a single voltage clamp pulse.

1. Sodium influx measurements were carried out on internally perfused squid giant axons under conditions of membrane potential control.2. The ratio ;measured extra sodium influx/calculated ionic influx from the inward current record' is close to unity and is independent of the duration of the rectangular pulse of membrane potential.3. The variation of the sodium permeability with time during the voltage clamp pulse is obtained by subtracting the sodium influx obtained from the ;tail' current record from the measured extra sodium influx.4. Evidence was obtained indicating that the measured change in sodium permeability during a sudden decrease of the membrane potential from its resting level involves two processes, namely, a transient increase in sodium permeability (activation), and a decrease in sodium permeability (inactivation).5. The extra influx of sodium during a voltage clamp pulse is not decreased by raising the internal sodium concentration from 0 to 100 mM, supporting the validity of the independence principle.

Animals↗
PubMed1970

Voltage clamp experiments on ventricular myocarial fibres.

1. A voltage clamp method utilizing a sucrose gap and glass microelectrodes was developed and used to study dog ventricular myocardial fibre bundles. The limitations and the reliability of this method are demonstrated by a series of tests.2. A dynamic sodium current, excited at membrane potentials more positive than -65 mV, was measured. The equilibrium potential for this large, rapid inward current depends directly on [Na](o), shifting 29.0 +/- 2.3 mV (+/- S.E. of mean), as opposed to a theoretically expected value of 30.6 mV, when [Na](o) is reduced to 31% of normal.3. Sodium current is inactivated by conditioning depolarizations. Complete inactivation occurs with conditioning potentials more positive than -45 mV, and 50% inactivation occurs at about -55 mV. The location of the inactivation curve shifts along the voltage axis, when [Ca](o) is varied between 0.2 and 7.2 mM.4. A second, much smaller and slower net inward current, with a threshold around -30 mV, and an equilibrium potential above +40 mV was also observed.5. The ;steady-state' current-voltage relationship (after 300-600 msec) exhibits inward-going (anomalous) rectification with negative slope between -50 and -25 mV.6. A small, very slowly developing component of outward current was observed at inside positive potentials. The equilibrium potential for this current, although slightly dependent on [K](o), is neither identical with the potassium equilibrium potential nor with the resting potential in normal Tyrode solution.7. Anatomical limitations, primarily resistance in the extracellular space within the bundle, prevent complete characterization of the rapid, large sodium current, but do not limit the application of the clamp method to the study of other, smaller and slower currents. The evidence for this is discussed extensively in the Appendix.

Animals↗
PubMed1976

Calcium-sodium antagonism on the frog's heart: a voltage-clamp study.

1. In double sucrose-gap voltage-clamped frog atrial fibres the influence of [Ca]o and [Na]o on membrane current and contraction was investigated. 2. The slow (secondary) inward current varied with [Ca]o but was almost insensitive to changes in [Na]o. In contrast, the phasic (transient) contraction initiated by the slow inward current was affected by both [Ca]o and [Na]o. 3. With moderate changes of [Ca]o and [Na]o from normal, the strength of phasic contraction at a given depolarization followed the [Ca]o/[Na]2o ratio approximately. This was best seen at membrane potentials near zero level. 4. Under the same conditions, tonic (sustained) contractions associated with prolonged depolarizations were strictly correlated to the [Ca]o/[Na]2o ratio at any potential. No interrelation between tonic tension and steady-state current was found. 5. With extensive changes in [Ca]o and [Na]o, the sensitivity of both phasic and tonic tension to the [Ca]o/[Na]2o ratio declined, the negative effect of [Na]o becoming smaller than was expected from this ratio. 6. In Na-free choline-Ringer, a strong contracture developed followed by a spontaneous relaxation. Starting from the relaxed state, application of depolarizing clamps gave rise to phasic contractions with a very slow relaxation while tonic contractions were apparently lacking. 7. The results are interpreted in terms of an energy-dependent carrier mechanism exchanging one Ca for two Na ions across the cell membrane. The model implies a strong asymmetry in the rate constants governing the chemical reactions on both sides of the membrane. The system is thought to operate close to equilibrium at any potential, thereby determining the steady level of myoplasmic Ca. The equilibrium itself is considered to shift upon depolarization. Assuming that [Na]i is constant, the steady level of [Ca]i is expected to be proportional to the [Ca]o/[Na]2o ratio, the scale factor being a function of membrane potential. 8. The carrier model suggests the occurrence of a depolarization-induced inward transfer of Ca which might be involved in the generation of tonic contractions. 9. The apparent lack of tonic contractions in the absence of external Na ions may be explained by a suppression of carrier-mediated Ca influx normally occurring upon depolarization. 10. The antagonistic effects of [Ca]o and [Na]o on phasic contraction are understood as being due to alterations of the Ca pumping system rather than changes in slow inward current.

Action Potentials↗
PubMed1977

Load clamp analysis of maximal force potential of mammalian cardiac muscle.

1. Abrupt alterations in load (load clamps) have been imposed on cat papillary muscle during isotonic shortening and relaxation of afterloaded twitch and tetanic contractions, to assess the maximal force potential for a given contractile state. 2. These load clamps were accompanied by an initial fast lengthening reflecting an undamped series compliance. Even when exceeding isometric twitch and tetanic force, these loads could be borne for a considerable time, accompanied by a slower lengthening after the initial extension of the series compliance. At sufficiently high loads the muscle was pulled out very rapidly; a maximal supra-isometric force potential was defined as the load the muscle could bear momentarily and this was measured at times throughout contraction and relaxation. 3. This maximal force potential was determined at different initial muscle lengths. Depending on the instantaneous loading conditions, various length-force relations were obtained from : (a) peak force values of isometric twitches at different starting lengths, (b) the shortest length reached during after loaded isotonic twitches, and (c) the forces obtained in overloaded isotonic twitch contractions. 4. These results are consistent with a crossbridge model in which the delayed lengthening during isotonic overloading is due to back rotation and detachment of attached crossbridges and in which the inital phase of spontaneous isotonic relaxation is governed by the same mechanism.

Animals↗
PubMed1979

Potassium currents in frog ventricular muscle: evidence from voltage clamp currents and extracellular K accumulation.

1. The single sucrose voltage clamp technique was used to control the membrane potential of strips of frog ventricular muscle and to measure the membrane current. The extracellular K accumulation was estimated from the after-potential observed after the release of the voltage clamp. 2. Comparing the time course of the membrane current to the time course of the development of the after-potential at different membrane potentials, it was found that all slow current changes are related to changes in the K current across the membrane. 3. Based on measurements of membrane current and the after-potential, the total membrane current was separated into two fractions: (a) the K current which gives rise to K accumulation and (b) the residual membrane current which is unrelated to K accumulation. The current-voltage relation for the residual membrane current is linear or slightly inwardly-rectifying. Residual current is zero at the resting potential and increases to about 1 microamperemeter/cm2 at -20 mV. 4. The measured membrane currents and after-potentials indicate qualitative differences between the K currents which dominate below and above -20 mV. More negative to -20 mV the after-potential develops rapidly while at potentials positive to -20 mV the after-potential develops with some delay. 5. The current dominating below -20 mV is inwardly-rectifying. The current-voltage relation has a maximum (about 2 microamperemeter/cm2) and a region with marked negative slope conductance. The outward current in the region of negative slope conductance is increased with increasing [K]o. 6. A model for the inwardly rectifying K current is described. The model accurately reproduces the shape of the measured current-voltage relations and their modification by alterations in the extracellular K concentration. The model is also compatible with the observation that all slow current changes below -20 mV are directly related to K accumulation. 7. The K current which dominates at potentials positive to -20 mV is activated by a potential and time dependent process which is unrelated to extracellular K accumulation. 8. Q10 for the magnitude of the inwardly rectifying K current is about 1.35 while the Q10 for the rate of increase of the time dependent K current is about 3--4. 9. Cs blocks the inwardly recitfying K current but has little effect on the time dependent K current. 10. The changes in the action potential duration caused by increasing the extracellular K concentration or addition of Cs to the perfusate can be explained by the effect of K and Cs on the inwardly rectifying K current.

Animals↗
PubMed1979

Three-micro-electrode voltage clamp experiments in calf cardiac Purkinje fibres: is slow inward current adequately measured?

1. The three-micro-electrode voltage clamp method (Adrian, Chandler & Hodgkin, 1970) was adapted for the study of regenerative inward currents in cardiac muscle. The adequacy of measurements of slow inward current in cardiac Purkinje fibres was assessed. 2. Membrane current density is reported simultaneously by total applied current (IT), along with a longitudinal voltage difference signal (delta V), recorded between two intracellular micro-electrodes. 3. Non-linear cable calculations show that delta V is a more faithful measure of membrane current density than IT as peak inward current increases. Quantitative agreement between delta V and IT only occurs when both signals report the membrane characteristics that would be obtained with an ideal longitudinal space clamp. 4. Agreement between delta V and IT is thus a useful criterion for satisfactory experimental measurements which we applied to the slow inward current. This component was elicited by depolarizing steps from a holding potential near =45 mV in the presence of tetrodotoxin. The IT signal was compared directly with delta V/R, where R is an effective longitudinal resistance that was experimentally determined. 5. delta V/R and IT showed very good agreement in both peak amplitude and time course at all potentials studied. 6. Radial non-uniformity during the measured peak slow inward current was estimated by calculations assuming clefts 200 A wide with a uniform distribution of ionic channels. The calculated voltage span from surface to centre was always less than 5 mV, and the measured I-V characteristics showed little distortion. 7. In another check, I-V characteristics and slow response membrane action potentials were compared. The measured peak current showed good agreement with the product (total preparation capacitance) x (rate of rise). 8. The experimental and theoretical analysis suggest that the measurements of slow inward current are a good approximation to genuine membrane properties.

Animals↗
PubMed1980

Calcium-dependent electrical activity and contraction of voltage-clamped frog single muscle fibres.

1. The electrical and mechanical activities of isolated frog muscle fibres have been simultaneously recorded under conditions which allow the development of a calcium permeability (chloride-free solution containing 72 mM-calcium levulinate instead of 115 mM-NaCl). 2. Long-lasting calcium action potentials and large and sustained contraction occur without inhibition of the potassium permeability. 3. The relationship observed between the slow inward calcium current and the amplitude of the contraction, under voltage-clamp conditions, resembles that found between IBa and tension in frog skeletal muscle and between ICa and the contraction in frog heart. A part of the mechanical response which is not abolished by manganese seems to be potential-dependent. 4. Integration of the current traces shows that the threshold of the contraction occurs at [Ca]1 near to 2.10(-6) M and that the contractile proteins are fully activated at [Ca]1 near to 10(-4) M, values which are in good agreement with those proposed by other authors. 5. The minimum calcium influx necessary to induce a detectable contraction is close to 4.8 p-moles/cm2. This value is 10-20 times larger than the calcium influx measured during a normal action potential. 6. On detubulated fibres the calcium permeability fails to develop: this indicates that this current originates from the T-system. The close correspondence between ICa and the contraction, and between the time course of the contraction at the end of the depolarizing steps suggests that the potential of the tubular membrane is better clamped than in normal physiological conditions.

Animals↗
PubMed1980

Voltage-clamp investigations of membrane currents underlying pace-maker activity in rabbit sino-atrial node.

1. Small preparations of spontaneously beating rabbit sino-atrial node have been investigated using the two micro-electrode voltage-clamp technique. 2. Hyperpolarizing clamp pulses given from holding potentials of about -45 mV reveal a time-dependent change of a membrane current, if, which is shown to overlap the pace-maker range (-65 mV to -45 mV) for these preparations. 3. The changes in if are shown to be quite distinct from the de-activation of the time-dependent outward current, iK. 4. The time-dependent changes of the if system increase during adrenaline application and therefore contribute to the chronotropic action of adrenaline on the heart. 5. Evidence for a link between slow inward current (iSi) and time-dependent outward current (iK) in rabbit sino-atrial node is presented and assessed.

Animals↗
PubMed1981

A study of pace-maker potential in rabbit sino-atrial node: measurement of potassium activity under voltage-clamp conditions.

1. A single sucrose-gap voltage-clamp technique was used to control the membrane potential and to measure current in rabbit sino-atrial (SA) strips. K+ activity in the extracellular space was simultaneously measured using K+-selective micro-electrodes. 2. Using double-barrelled K+ selective micro-electrodes it was possible to measure the time course of accumulation or depletion of K+ accompanying a single action potential without complications arising from mechanical or electrical artifacts. 3. K+ activity in the extracellular space increased during the action potential and then decreased to base-line levels during the diastolic depolarization phase. Single beat accumulations of 0.1-0.4 M could be measured. 4. The magnitude of accumulation or depletion of K+ depended upon the membrane potential such that K+ accumulated at potentials positive to -50 mV (K+ efflux greater than K+ uptake) and was depleted from the extracellular space at potentials negative to -50 mV (K+ efflux less than K+ uptake). 5. The rate of K+ depletion was fairly constant during the time course of a clamp step within the range of diastolic depolarization (-55 to -75 mV) even though the accompanying membrane current showed marked time-dependent kinetics. 6. The total membrane conductance measured during the time course of the diastolic depolarization or during the time course of activation of time-dependent 'pace-maker' current remained fairly constant or increased. 7. No reversal potential for the time-dependent 'pace-maker' current could be measured at EK in solutions containing 2.7, 5.4 and 8.1 mM-K+. 8. These results do not support the turn-off a K+ conductance as the primary mechanisms for the generation of the pace-maker potential in SA nodal tissue; rather the results are more consistent with the idea that activation of an inward current, with large positive equilibrium potential, is responsible for pace-making activity.

Animals↗
PubMed1981

Simultaneous changes in the equilibrium potential and potassium conductance in voltage clamped Ranvier node in the frog.

1. In voltage clamped myelinated nerve fibres, the K+ conductance has been calculated from current recordings obtained in low and high K+ media, taking into account the changes in EK resulting from accumulation of depletion of K+ ions near to nodal membrane. 2. At the end of a depolarization, the instantaneous K+ current reverses at a potential (instantaneous reversal potential) differing from the Nernst potential calculated using the external and internal bulk concentrations (theoretical Nernst potential). During a depolarization, EK, as estimated from the instantaneous reversal potential, changes continuously. This change depends on the size, the duration and the direction of the time dependent K+ current. The variation of EK is attributed to continuous changes in K+ concentration near the membrane during voltage pulses which turn on the K+ conductance. 3. The chord conductance [GK = IK/(E-EK), as calculated using the instantaneous reversal potential values for EK, has been analysed as a function of time and membrane potential. As previously reported it increases with the initial K+ concentration in the external medium. 4. The time course of the K+ current depends on both the kinetics of the conductance increase and the rate of change in the driving force for K. The kinetics of the conductance increase can satisfactorily be described by a single exponential function following a delay after the onset of the depolarizing voltage clamp pulse. 5. This delay increases when the holding potential is made more negative. It decreases with membrane depolarization and it is independent of the external K+ concentration. At a given membrane potential, the turning on of the K+ conductance is found to be faster at high than at low external K+ concentrations. 6. At repolarization the turning off of the conductance cannot be described by a single exponential function. It is faster at low than at high external K+ concentrations. 7. The results suggest that the change in K+ conductance proceeds in a multi-step transition or (and) that the K+ conductance is determined by several types of K+ channels.

Animals↗
PubMed1981

Single glutamate-activated channels recorded from locust muscle fibres with perfused patch-clamp electrodes.

1. Glutamate-activated single channels have been examined with conventional and internally perfused patch-clamp electrodes applied to the extrajunctional membrane of locust muscle fibres which were usually treated with concanavalin A to reduce desensitization. Channels opened by glutamate and other agonists have been compared.2. Recording patches were selected where there appeared to be only one active channel under the pipette. The conductance for single glutamate-activated channels was 150 pS and was not markedly dependent on clamp potential. The lifetimes of the channels were usually exponentially distributed with a mean of tau(glutamate) = 2.3 +/- 0.12 msec, T = 23 degrees C, V(m) = -60 mV.3. Channels opened by fluoroglutamate had a mean lifetime of tau(fluoroglutamate) = 1.4 +/- 0.1 msec; channels opened by quisqualate had a mean lifetime of tau(quisqualate) = 6.4 +/- 1.0 msec. The conductances of channels opened by fluoroglutamate, quisqualate and glutamate were not significantly different.4. The behaviour of individual receptor-channel complexes has been examined at various concentrations of glutamate. Drug solutions were applied through an internal perfusion pipette which allowed exchange of the solution in the patch-electrode tip within 10 sec. The distribution of channel closed times could be fitted with a single exponential. Channel lifetime was not markedly dependent on glutamate concentration (30-600 mum) whereas the channel closed time decreased with increasing glutamate concentration.5. The reciprocal of channel closed time vs. glutamate concentration had a slope value of 1.85 on logarithmic co-ordinates. The approximately second power dependence of net forward reaction rate on glutamate concentration suggests that at least two glutamate molecules activate a single receptor-channel complex.6. The apparent dissociation constant for the glutamate-receptor complex is large, being about 300-500 muM. If the receptors have an equally low affinity for neurally released transmitter, then only a small amount of the transmitter packet is expected to bind to receptors. Quisqualate and glutamate have similar receptor affinities whereas receptor affinity for fluoroglutamate is smaller.

Animals↗
PubMed1982

A patch-clamp study of bovine chromaffin cells and of their sensitivity to acetylcholine.

1. Bovine chromaffin cells were enzymatically isolated and kept in short term tissue culture. Their electrical properties were studied using recent advances of the patch-clamp technique (Hamill, Marty, Neher, Sakmann & Sigworth, 1981). 2. When a patch pipette was sealed tightly to a chromaffin cell ('cell-attached configuration') current wave forms due to intracellular action potentials could be observed. The frequency of the wave forms was altered by changing the pipette potential. When acetylcholine was present in the pipette solution, acetylcholine-induced single channel currents were evident in the patch recording. Action potential wave forms were then often seen to follow acetycholine-induced single channel currents. 3. In the cell-attached configuration, large single channel current events did not resemble square pulses but showed exponential relaxations with time constants of the order of 50 ms. 4. After rupture of the patch of membrane, the pipette--cell seal remained stable ('whole-cell recording', Hamill et al. 1981). Chromaffin cells were found to have a resting potential of -50 to -80 mV, and an input resistance around 5 G omega. The high cell resistance accounts for the relaxing currents evident in the cell-attached configuration. 5. In the best cases, the effective time constant of the voltage clamp in the whole-cell recording mode was 15 microseconds. Exchange of small ions such as Na+ ions between pipette and cell interior solutions was then complete within 15 s. 6. Acetylcholine-induced currents were obtained at various acetylcholine concentrations. Single acetylcholine-induced channels had a slope conductance of 44 pS between -100 and -55 mV, and a mean duration of 27 ms at -80 mV (at room temperature).

Acetylcholine↗