Ionic currents in identified swimmeret motor neurones of the crayfish Pacifastacus leniusculus

1995 ◽  
Vol 198 (7) ◽  
pp. 1483-1492 ◽  
Author(s):  
A Chrachri
Keyword(s):  
Time Course ◽  
Outward Current ◽  
Rhythmic Activity ◽  
Ionic Currents ◽  
Power Stroke ◽  
Transient Outward Current ◽  
Patch Clamp Technique ◽  
Outward Currents ◽  
Inward Currents ◽  
Motor Neurones

Ionic currents from freshly isolated and identified swimmeret motor neurones were characterized using a whole-cell patch-clamp technique. Two outward currents could be distinguished. A transient outward current was elicited by delivering depolarizing voltage steps from a holding potential of -80 mV. This current was inactivated by holding the cells at a potential of -40 mV and was also blocked completely by 4-aminopyridine. A second current had a sustained time course and continued to be activated at a holding potential of -40 mV. This current was partially blocked by tetraethylammonium. These outward currents resembled two previously described potassium currents: the K+ A-current and the delayed K+ rectifier current respectively. Two inward currents were also detected. A fast transient current was blocked by tetrodotoxin and inactivated at holding potential of -40 mV, suggesting that this is an inward Na+ current. A second inward current had a sustained time course and was affected neither by tetrodotoxin nor by holding the cell at a potential of -40 mV. This current was substantially enhanced by the addition of Ba2+ to the bath or when equimolar Ba2+ replaced Ca2+ as the charge carrier. Furthermore, this current was significantly suppressed by nifedipine. All these points suggest that this is an L-type Ca2+ current. Bath application of nifedipine into an isolated swimmeret preparation affected both the frequency of the swimmeret rhythm and the duration of power-stroke activity, suggesting an important role for the inward Ca2+ current in maintaining a regular swimmeret rhythmic activity in crayfish.

Inhibition of metabolism abolishes transient outward current in rabbit atrial myocytes

1994 ◽  
Vol 266 (1) ◽  
pp. H182-H190 ◽  
Author(s):  
A. Ogbaghebriel ◽  
A. Shrier
Keyword(s):  
Steady State ◽  
Patch Clamp ◽  
Potassium Current ◽  
Outward Current ◽  
Transient Outward Current ◽  
Atrial Myocytes ◽  
Patch Clamp Technique ◽  
Outward Currents ◽  
Inward Currents ◽  
Inhibition Of Metabolism

Outward currents were measured in single rabbit atrial myocytes using the whole cell configuration of the patch-clamp technique in the presence of tetrodotoxin (5–10 microM) and MnCl2 (2 mM) to block inward currents. Depolarizing voltage-clamp steps from a holding potential of -80 mV elicited a predominant 4-aminopyridine (4-AP)-sensitive transient outward current (Ito). Inhibitors of oxidative metabolism, 2,4-dinitrophenol (DNP; 100 microM) and cyanide (3 mM) abolished Ito and caused a large increase in the steady-state outward current. This steady-state outward current was inhibited by glibenclamide (5 microM), a blocker of the ATP-regulated potassium current (IKATP). In the presence of DNP, glibenclamide (5 microM) not only inhibited IKATP but also partially restored Ito. Absence of ATP from the pipette produced effects on outward currents similar to those induced by DNP or cyanide. We conclude that metabolic inhibition abolishes Ito in rabbit atrial myocytes and suggest that ATP may be required for the activation of the channel.

scholarly journals Effect of Auxin (IAA) on the Fast Vacuolar (FV) Channels in Red Beet (Beta vulgaris L.) Taproot Vacuoles

2020 ◽  
Vol 21 (14) ◽  
pp. 4876
Author(s):  
Zbigniew Burdach ◽  
Agnieszka Siemieniuk ◽  
Waldemar Karcz
Keyword(s):  
Single Channel ◽  
Outward Current ◽  
K Channel ◽  
Single Channels ◽  
Patch Clamp Technique ◽  
Open Probability ◽  
Inward Current ◽  
Bath Solution ◽  
Outward Currents ◽  
Inward Currents

In contrast to the well-studied effect of auxin on the plasma membrane K+ channel activity, little is known about the role of this hormone in regulating the vacuolar K+ channels. Here, the patch-clamp technique was used to investigate the effect of auxin (IAA) on the fast-activating vacuolar (FV) channels. It was found that the macroscopic currents displayed instantaneous currents, which at the positive potentials were about three-fold greater compared to the one at the negative potentials. When auxin was added to the bath solution at a final concentration of 1 µM, it increased the outward currents by about 60%, but did not change the inward currents. The imposition of a ten-fold vacuole-to-cytosol KCl gradient stimulated the efflux of K+ from the vacuole into the cytosol and reduced the K+ current in the opposite direction. The addition of IAA to the bath solution with the 10/100 KCl gradient decreased the outward current and increased the inward current. Luminal auxin reduced both the outward and inward current by approximately 25% compared to the control. The single channel recordings demonstrated that cytosolic auxin changed the open probability of the FV channels at the positive voltages to a moderate extent, while it significantly increased the amplitudes of the single channel outward currents and the number of open channels. At the positive voltages, auxin did not change the unitary conductance of the single channels. We suggest that auxin regulates the activity of the fast-activating vacuolar (FV) channels, thereby causing changes of the K+ fluxes across the vacuolar membrane. This mechanism might serve to tightly adjust the volume of the vacuole during plant cell expansion.

Transient potassium currents in avian sensory neurons

1990 ◽  
Vol 63 (4) ◽  
pp. 725-737 ◽  
Author(s):  
S. K. Florio ◽  
C. D. Westbrook ◽  
M. R. Vasko ◽  
R. J. Bauer ◽  
J. L. Kenyon
Keyword(s):  
Single Channel ◽  
Outward Current ◽  
Potassium Currents ◽  
Delayed Rectifier ◽  
Transient Outward Current ◽  
Single Channels ◽  
Patch Clamp Technique ◽  
Small Component ◽  
Whole Cell ◽  
Outward Currents

1. We used the patch-clamp technique to study voltage-activated transient potassium currents in freshly dispersed and cultured chick dorsal root ganglion (DRG) cells. Whole-cell and cell-attached patch currents were recorded under conditions appropriate for recording potassium currents. 2. In whole-cell experiments, 100-ms depolarizations from normal resting potentials (-50 to -70 mV) elicited sustained outward currents that inactivated over a time scale of seconds. We attribute this behavior to a component of delayed rectifier current. After conditioning hyperpolarizations to potentials negative to -80 mV, depolarizations elicited transient outward current components that inactivated with time constants in the range of 8-26 ms. We attribute this behavior to a transient outward current component. 3. Conditioning hyperpolarizations increased the rate of activation of the net outward current implying that the removal of inactivation of the transient outward current allows it to contribute to early outward current during depolarizations from negative potentials. 4. Transient current was more prominent on the day the cells were dispersed and decreased with time in culture. 5. In cell-attached patches, single channels mediating outward currents were observed that were inactive at resting potentials but were active transiently during depolarizations to potentials positive to -30 mV. The probability of channels being open increased rapidly (peaking within approximately 6 ms) and then declined with a time constant in the range of 13-30 ms. With sodium as the main extracellular cation, single-channel conductances ranged from 18 to 32 pS. With potassium as the main extracellular cation, the single-channel conductance was approximately 43 pS, and the channel current reversed near 0 mV, as expected for a potassium current. 6. We conclude that the transient potassium channels mediate the component of transient outward current seen in the whole-cell experiments. This current is a relatively small component of the net current during depolarizations from normal resting potentials, but it can contribute significant outward current early in depolarizations from hyperpolarized potentials.

scholarly journals Properties of "creep currents" in single frog atrial cells.

1986 ◽  
Vol 87 (6) ◽  
pp. 833-855 ◽  
Author(s):  
J R Hume ◽  
A Uehara
Keyword(s):  
Time Course ◽  
Outward Current ◽  
Membrane Current ◽  
K Channel ◽  
Transient Outward Current ◽  
Ca Channel ◽  
Purkinje Fibers ◽  
Atrial Cells ◽  
Cardiac Purkinje Fibers ◽  
Inward Currents

Changes in membrane current in response to an elevation of [Na]i were studied in enzymatically dispersed frog atrial cells. Na loading by either intracellular dialysis or exposure to the Na ionophore monensin produces changes in membrane current that resemble the "creep currents" originally observed in cardiac Purkinje fibers during exposure to low-K solutions. Na loading induces a transient outward current during depolarizing voltage-clamp pulses, followed by an inward current in response to repolarization back to the holding potential. In contrast to cardiac Purkinje fibers, Na loading of frog atrial cells induces creep currents without accompanying transient inward currents. Creep currents induced by Na loading are insensitive to K channel antagonists like Cs and 4-aminopyridine; they are not influenced by doses of Ca channel antagonists that abolish iCa, but are sensitive to changes in [Ca]o or [Na]o. A comparison of the time course of development of inward creep currents are not tail currents associated with iCa. Inward creep currents can also be induced by experimental interventions that increase the iCa amplitude. Exposure to isoproterenol enhances the iCa amplitude and induces inward creep currents; both can be attenuated by Ca channel antagonists. Both inward and outward creep currents are blocked by low doses of La, independently of La's ability to block iCa. It is concluded that (a) creep currents are not mediated by voltage-gated Na, Ca, or K channels or by an electrogenic Na,K pump; (b) inward creep currents induced either by Na loading or in response to an increase in the amplitude of iCa are triggered by an elevation of [Ca]i; and (c) creep currents may be generated by either an electrogenic Na/Ca exchange mechanism or by a nonselective cation channel activated by [Ca]i.

Ca(2+)-dependent outward currents in myocytes from epicardial border zone of 5-day infarcted canine heart

1997 ◽  
Vol 273 (3) ◽  
pp. H1386-H1394 ◽  
Author(s):  
R. Aggarwal ◽  
J. Pu ◽  
P. A. Boyden
Keyword(s):  
Action Potentials ◽  
Time Course ◽  
Outward Current ◽  
Border Zone ◽  
Disulfonic Acid ◽  
Transient Outward Current ◽  
Canine Heart ◽  
Whole Cell Patch Clamp ◽  
Outward Currents ◽  
Transmembrane Action Potentials

Myocytes from the epicardial border zone (EBZ) of the 5-day infarcted canine heart (IZ) have abnormal transmembrane action potentials, reduced L-type Ca2+ currents (ICa,L) and altered intracellular Ca2+ (Cai) transients compared with those of normal epicardial myocytes (NZ). We hypothesized that altered Cai cycling might be reflected in differences in Cai-dependent outward currents (Ito2). We recorded Ito2 in NZ and IZ using whole cell patch-clamp techniques. Ito2 was defined as the amplitude of the 4-aminopyridine-resistant transient outward current that was blocked by 200 microM 4,4'-diisothiocyanostilbene-2,2'-disulfonic acid (DIDS) or DIDS+ ryanodine (2 microM). Ito2 were present in both NZ and IZ, but peak density was significantly reduced in IZ, particularly at positive plateau voltages. Time course of decay of Ito2 was biexponential and similar in NZ and IZ. A given peak ICa,L was usually associated with a smaller peak Ito2 in IZ. These differences were exaggerated when Ito2 and Cai transients were determined in rapidly paced cells. In summary, myocytes surviving in the EBZ of the infarcted heart have Ito2, yet they are reduced in density and can vary, particularly at fast pacing rates.

scholarly journals Voltage-Activated Ionic Currents in Myoepithelial Cells Isolated from the Sea Anemone Calliactis Tricolor

1991 ◽  
Vol 161 (1) ◽  
pp. 333-346 ◽  
Author(s):  
MOLLY A. HOLMAN ◽  
PETER A. V. ANDERSON
Keyword(s):  
Action Potentials ◽  
Outward Current ◽  
Ionic Currents ◽  
Myoepithelial Cells ◽  
Sea Anemone ◽  
Calcium Currents ◽  
Transient Outward Current ◽  
Ionic Selectivity ◽  
Patch Clamp Technique ◽  
Steady State Current

Myoepithelial cells were isolated from the apical ends of mesenteries of the sea anemone Calliactis tricolor and examined using the whole-cell configuration of the patch-clamp technique. The isolation procedure produced cell fragments that were contractile and produced action potentials when depolarized. These action potentials are formed by a complex array of ionic currents consisting of at least one, and possibly two, inward calcium currents and four outward potassium currents. The ionic selectivity of the calcium currents was Ca2+>Sr2+>Ba2+. Outward currents consisted of a calcium-dependent outward current and three voltage-activated currents, including a 4-aminopyridine-sensitive current, a transient outward current and a steady-state current.

scholarly journals Properties of calcium and potassium currents of clonal adrenocortical cells.

1989 ◽  
Vol 93 (3) ◽  
pp. 495-519 ◽  
Author(s):  
L Tabares ◽  
J Ureña ◽  
J López-Barneo
Keyword(s):  
Time Course ◽  
Outward Current ◽  
Ionic Currents ◽  
Ca Current ◽  
Closing Time ◽  
Patch Clamp Technique ◽  
Adrenocortical Cells ◽  
Activation Threshold ◽  
Activation Kinetics ◽  
K Current

The ionic currents of clonal Y-1 adrenocortical cells were studied using the whole-cell variant of the patch-clamp technique. These cells had two major current components: a large outward current carried by K ions, and a small inward Ca current. The Ca current depended on the activity of two populations of Ca channels, slow (SD) and fast (FD) deactivating, that could be separated by their different closing time constants (at -80 mV, SD, 3.8 ms, and FD, 0.13 ms). These two kinds of channels also differed in (a) activation threshold (SD, approximately -50 mV; FD, approximately -20 mV), (b) half-maximal activation (SD, between -15 and -10 mV; FD between +10 and +15 mV), and (c) inactivation time course (SD, fast; FD, slow). The total amplitude of the Ca current and the proportion of SD and FD channels varied from cell to cell. The amplitude of the K current was strongly dependent on the internal [Ca2+] and was almost abolished when internal [Ca2+] was less than 0.001 microM. The K current appeared to be independent, or only slightly dependent, of Ca influx. With an internal [Ca2+] of 0.1 microM, the activation threshold was -20 mV, and at +40 mV the half-time of activation was 9 ms. With 73 mM external K the closing time constant at -70 mV was approximately 3 ms. The outward current was also modulated by internal pH and Mg. At a constant pCa gamma a decrease of pH reduced the current amplitude, whereas the activation kinetics were not much altered. Removal of internal Mg produced a drastic decrease in the amplitude of the Ca-activated K current. It was also found that with internal [Ca2+] over 0.1 microM the K current underwent a time-dependent transformation characterized by a large increase in amplitude and in activation kinetics.

scholarly journals Calcium currents in embryonic and neonatal mammalian skeletal muscle.

1988 ◽  
Vol 91 (6) ◽  
pp. 781-798 ◽  
Author(s):  
K G Beam ◽  
C M Knudson
Keyword(s):  
Time Course ◽  
Sodium Current ◽  
Primary Cultures ◽  
Ionic Currents ◽  
Cell Types ◽  
Calcium Currents ◽  
Mammalian Skeletal Muscle ◽  
Patch Clamp Technique ◽  
Complete Inactivation ◽  
Inward Currents

The whole-cell patch-clamp technique was used to study the properties of inward ionic currents found in primary cultures of rat and mouse skeletal myotubes and in freshly dissociated fibers of the flexor digitorum brevis muscle of rats. In each of these cell types, test depolarizations from the holding potential (-80 or -90 mV) elicited three distinct inward currents: a sodium current (INa) and two calcium currents. INa was the dominant inward current: under physiological conditions, the maximum inward INa was estimated to be at least 30-fold larger than either of the calcium currents. The two calcium currents have been termed Ifast and Islow, corresponding to their relative rates of activation. Ifast was activated by test depolarizations to around -40 mV and above, peaked in 10-20 ms, and decayed to baseline in 50-100 ms. Islow was activated by depolarizations to approximately 0 mV and above, peaked in 50-150 ms, and decayed little during a 200-ms test pulse. Ifast was inactivated by brief, moderate depolarizations; for a 1-s change in holding potential, half-inactivation occurred at -55 to -45 mV and complete inactivation occurred at -40 to -30 mV. Similar changes in holding potential had no effect on Islow. Islow was, however, inactivated by brief, strong depolarizations (e.g., 0 mV for 2 s) or maintained, moderate depolarizations (e.g., -40 mV for 60 s). Substitution of barium for calcium had little effect on the magnitude or time course of either Ifast or Islow. The same substitution shifted the activation curve for Islow approximately 10 mV in the hyperpolarizing direction without affecting the activation of Ifast. At low concentrations (50 microM), cadmium preferentially blocked Islow compared with Ifast, while at high concentrations (1 mM), it blocked both Ifast and Islow completely. The dihydropyridine calcium channel antagonist (+)-PN 200-110 (1 microM) caused a nearly complete block of Islow without affecting Ifast. At a holding potential of -80 mV, the half-maximal blocking concentration (K0.5) for the block of Islow by (+)-PN 200-110 was 182 nM. At depolarized holding potentials that inactivated Islow by 35-65%, K0.5 decreased to 5.5 nM.

Voltage Clamp Studies on Insect Skeletal Muscle: II. The Outward Currents

1981 ◽  
Vol 92 (1) ◽  
pp. 13-22
Author(s):  
DAISUKE YAMAMOTO ◽  
HIROSHI WASHIO
Keyword(s):  
Voltage Clamp ◽  
Time Course ◽  
Reversal Potential ◽  
Outward Current ◽  
Transient Outward Current ◽  
Muscle Fibres ◽  
Activation Process ◽  
Outward Currents ◽  
K Concentration ◽  
Insect Skeletal Muscle

Two components of outward currents were investigated under voltage clamp conditions in Tenebrio muscle fibres. The instantaneous current-voltage relation for the transient outward current showed outward rectification. The tail currents for the delayed outward currents were made up of either one or two exponential components. The activation process for the delayed current was analysed using positive tails that decayed with a simple exponential time course. The delayed current was half-activated at about + 35 mV. Two rate constants for activation are both monotonic functions of membrane potential. The reversal potential for the delayed current was only partially dependent on the external K-concentration. The role of the two outward currents in the production of the action potential was discussed.

Current-Voltage Relations in the Isolated Giant Axon of the Cockroach Under Voltage-Clamp Conditions

1967 ◽  
Vol 47 (2) ◽  
pp. 343-355
Author(s):  
Y. PICHON ◽  
J. BOISTEL
Keyword(s):  
Action Potentials ◽  
Outward Current ◽  
Node Of Ranvier ◽  
Ionic Currents ◽  
Giant Axon ◽  
Inward Current ◽  
Outward Currents ◽  
Current Voltage ◽  
Inward Currents ◽  
Na Ions

1. An experimental method of recording and controlling the membrane potential of a small area of the membrane of the cockroach giant axon is described. 2. The recorded action potentials were essentially similar to those previously recorded by other methods. 3. The membrane currents resemble those reported for the squid axon, the node of Ranvier in frog nerve and the lobster giant axon. 4. Small cathodal polarizations gave only small outward currents; larger depolarizations (10-100 mV.) gave an initial inward current which changed into a delayed outward current. 5. The initial inward current attained a maximum with depolarizing pulses of 40-50 mV. and showed a reversed, outward, flow of about 100 mV. 6. Delayed outward currents increased continuously with increasing impulse voltage. 7. The initial inward current was larger when the pulse was preceded by an hyperpolarizing prepulse. 8. It is concluded that, although the early inward currents were in all probability related to Na+ ions and the delayed outward currents to K+ ions, the possible participation of Ca2+ and Cl- ions to the ionic currents cannot be excluded.

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