Characteristics of a fast transient outward current in guinea pig trigeminal motoneurons

1995 ◽  
Vol 695 (2) ◽  
pp. 217-226 ◽  
Author(s):  
Chie-fang Hsiao ◽  
Scott H. Chandler
Keyword(s):  
Guinea Pig ◽  
Outward Current ◽  
Transient Outward Current ◽  
Trigeminal Motoneurons ◽  
Fast Transient

scholarly journals Diverse Ionic Currents and Electrical Activity of Cultured Myenteric Neurons From the Guinea Pig Proximal Colon

2000 ◽  
Vol 83 (3) ◽  
pp. 1253-1263 ◽  
Author(s):  
Fivos Vogalis ◽  
Kirk Hillsley ◽  
Terence K. Smith
Keyword(s):  
Patch Clamp ◽  
Guinea Pig ◽  
Action Potential ◽  
Action Potentials ◽  
Outward Current ◽  
Proximal Colon ◽  
Equilibrium Potential ◽  
Transient Outward Current ◽  
Myenteric Neurons ◽  
Fast Transient

The aim of this study was to perform a patch-clamp analysis of myenteric neurons from the guinea pig proximal colon. Neurons were enzymatically dispersed, cultured for 2–7 days, and recorded from using whole cell patch clamp. The majority of cells fired phasically, whereas about one-quarter of the neurons fired in a tonic manner. Neurons were divided into three types based on the currents activated. The majority of tonically firing neurons lacked an A-type current, but generated a large fast transient outward current that was associated with the rapid repolarizing phase of an action potential. The fast transient outward current was dependent on calcium entry and was blocked by tetraethylammonium. Cells that expressed both an A-type current and a fast transient outward current were mostly phasic. Depolarization of these cells to suprathreshold potentials from less than −60 mV failed to trigger action potentials, or action potentials were only triggered after a delay of >50 ms. However, depolarizations from more positive potentials triggered action potentials with minimal latency. Neurons that expressed neither the A-type current or the fast transient outward current were all phasic. Sixteen percent of neurons were similar to AH/type II neurons in that they generated a prolonged afterhyperpolarization following an action potential. The current underlying the prolonged afterhyperpolarization showed weak inward rectification and had a reversal potential near the potassium equilibrium potential. Thus cultured isolated myenteric neurons of the guinea pig proximal colon retain many of the diverse properties of intact neurons. This preparation is suitable for further biophysical and molecular characterization of channels expressed in colonic myenteric neurons.

Existence of a transient outward K+ current in guinea pig cardiac myocytes

2000 ◽  
Vol 279 (1) ◽  
pp. H130-H138 ◽  
Author(s):  
Gui-Rong Li ◽  
Baofeng Yang ◽  
Haiying Sun ◽  
Clive M. Baumgarten
Keyword(s):  
Guinea Pig ◽  
Ventricular Myocytes ◽  
Outward Current ◽  
Resting Potential ◽  
Transient Outward Current ◽  
Time Constants ◽  
Zero Current ◽  
Steady State Inactivation ◽  
K Current ◽  
External K

A novel transient outward K+current that exhibits inward-going rectification ( I to.ir) was identified in guinea pig atrial and ventricular myocytes. I to.ir was insensitive to 4-aminopyridine (4-AP) but was blocked by 200 μmol/l Ba2+or removal of external K+. The zero current potential shifted 51–53 mV/decade change in external K+. I to.ir density was twofold greater in ventricular than in atrial myocytes, and biexponential inactivation occurs in both types of myocytes. At −20 mV, the fast inactivation time constants were 7.7 ± 1.8 and 6.1 ± 1.2 ms and the slow inactivation time constants were 85.1 ± 14.8 and 77.3 ± 10.4 ms in ventricular and atrial cells, respectively. The midpoints for steady-state inactivation were −36.4 ± 0.3 and −51.6 ± 0.4 mV, and recovery from inactivation was rapid near the resting potential (time constants = 7.9 ± 1.9 and 8.8 ± 2.1 ms, respectively). I to.ir was detected in Na+-containing and Na+-free solutions and was not blocked by 20 nmol/l saxitoxin. Action potential clamp revealed that I to.ir contributed an outward current that activated rapidly on depolarization and inactivated by early phase 2 in both tissues. Although it is well known that 4-AP-sensitive transient outward current is absent in guinea pig, this Ba2+-sensitive and 4-AP-insensitive K+ current has been overlooked.

Transient voltage and calcium-dependent outward currents in hippocampal CA3 pyramidal neurons

1985 ◽  
Vol 53 (4) ◽  
pp. 1038-1058 ◽  
Author(s):  
K. L. Zbicz ◽  
F. F. Weight
Keyword(s):  
Time Course ◽  
Pyramidal Neurons ◽  
Sympathetic Neurons ◽  
Outward Current ◽  
Transient Current ◽  
Transient Outward Current ◽  
Molluscan Neurons ◽  
Voltage Sensitivity ◽  
Transient Currents ◽  
Fast Transient

Membrane currents activated by step changes in membrane potential were studied in hippocampal pyramidal neurons of region CA3 using the single microelectrode voltage-clamp technique. The transient outward current activated by depolarizing steps appeared to be composed of two transient currents that could be distinguished by differences in voltage sensitivity, time course, and pharmacological sensitivity. The more slowly decaying current was activated by voltage steps positive to -60 mV and declined exponentially with a time constant between 200 and 400 ms. This current inactivated as the holding potential was made more positive over the range of -75 to -45 mV and was 50% inactivated near -60 mV. The more slowly decaying transient current was selectively blocked by 0.5 mM 4-aminopyridine (4-AP) but not by 5-10 mM tetraethylammonium (TEA) or 2-5 mM Mn2+. The second transient current had a much faster time course than the 4-AP-sensitive current, having a duration of 5-20 ms. This very fast transient current was observed during potential steps positive to -45 mV. The fast transient current was inactivated when the holding potential was made positive to -45 mV. The amplitude of the fast transient current was greatly reduced by the application of 4 mM Mn2+ or Ca2+-free artificial cerebrospinal fluid (CSF). The fast transient current appeared to be unaffected by 0.5 mM 4-AP but was greatly reduced by 10 mM TEA. These results suggest that the transient outward current observed during depolarizing steps is composed of at least two distinct transient currents. The more slowly decaying current resembles the A-current originally described in molluscan neurons (9, 32, 42) in voltage sensitivity, time course, and pharmacological sensitivity. The faster transient current resembles a fast, Ca2+-dependent transient current previously observed in bull-frog sympathetic neurons (5, 27).

Current- and Voltage-Clamp Recordings and Computer Simulations of Kenyon Cells in the Honeybee

2004 ◽  
Vol 92 (4) ◽  
pp. 2589-2603 ◽  
Author(s):  
Daniel G. Wüstenberg ◽  
Milena Boytcheva ◽  
Bernd Grünewald ◽  
John H. Byrne ◽  
Randolf Menzel ◽  
...  
Keyword(s):  
Voltage Clamp ◽  
Mushroom Body ◽  
Outward Current ◽  
Delayed Rectifier ◽  
Transient Outward Current ◽  
Insect Brain ◽  
Type Model ◽  
Kenyon Cells ◽  
Fast Transient

The mushroom body of the insect brain is an important locus for olfactory information processing and associative learning. The present study investigated the biophysical properties of Kenyon cells, which form the mushroom body. Current- and voltage-clamp analyses were performed on cultured Kenyon cells from honeybees. Current-clamp analyses indicated that Kenyon cells did not spike spontaneously in vitro. However, spikes could be elicited by current injection in approximately 85% of the cells. Of the cells that produced spikes during a 1-s depolarizing current pulse, approximately 60% exhibited repetitive spiking, whereas the remaining approximately 40% fired a single spike. Cells that spiked repetitively showed little frequency adaptation. However, spikes consistently became broader and smaller during repetitive activity. Voltage-clamp analyses characterized a fast transient Na+ current ( INa), a delayed rectifier K+ current ( IK,V), and a fast transient K+ current ( IK,A). Using the neurosimulator SNNAP, a Hodgkin–Huxley-type model was developed and used to investigate the roles of the different currents during spiking. The model led to the prediction of a slow transient outward current ( IK,ST) that was subsequently identified by reevaluating the voltage-clamp data. Simulations indicated that the primary currents that underlie spiking are INa and IK,V, whereas IK,A and IK,ST primarily determined the responsiveness of the model to stimuli such as constant or oscillatory injections of current.

scholarly journals Ca2+ Overload Evokes a Transient Outward Current in Guinea-Pig Ventricular Myocytes

2002 ◽  
Vol 66 (1) ◽  
pp. 87-92 ◽  
Author(s):  
Ichirota Nakajima ◽  
Hiroyuki Watanabe ◽  
Kenji Iino ◽  
Takashi Saito ◽  
Mamoru Miura
Keyword(s):  
Guinea Pig ◽  
Ventricular Myocytes ◽  
Outward Current ◽  
Transient Outward Current

Characterization of a fast transient outward current in neocortical neurons from epilepsy patients

2004 ◽  
Vol 75 (6) ◽  
pp. 807-816 ◽  
Author(s):  
C. Rüschenschmidt ◽  
R. Köhling ◽  
M. Schwarz ◽  
H. Straub ◽  
A. Gorji ◽  
...  
Keyword(s):  
Outward Current ◽  
Transient Outward Current ◽  
Neocortical Neurons ◽  
Fast Transient

Transient outward current carried by inwardly rectifying K+ channels in guinea pig ventricular myocytes dialyzed with low-K+ solution

2004 ◽  
Vol 287 (5) ◽  
pp. C1396-C1403 ◽  
Author(s):  
Pavel Zhabyeyev ◽  
Tatsuya Asai ◽  
Sergey Missan ◽  
Terence F. McDonald
Keyword(s):  
Guinea Pig ◽  
Ventricular Myocytes ◽  
Outward Current ◽  
Transient Outward Current ◽  
K Channels ◽  
Voltage Gated ◽  
Voltage Gated Channels ◽  
Inwardly Rectifying ◽  
Low K ◽  
External K

There have been periodic reports of nonclassic (4-aminopyridine insensitive) transient outward K+ current in guinea pig ventricular myocytes, with the most recent one describing a novel voltage-gated inwardly rectifying type. In the present study, we have investigated a transient outward current that overlaps inward Ca2+ current ( ICa,L) in myocytes dialyzed with 10 mM K+ solution and superfused with Tyrode’s solution. Although depolarizations from holding potential ( Vhp) −40 to 0 mV elicited relatively small inward ICa,L in these myocytes, removal of external K+ or addition of 0.2 mM Ba2+ more than doubled the amplitude of the current. The basis of the enhancement of ICa,L was the suppression of a large transient outward K+ current. Similar enhancement was observed when Vhp was moved to −80 mV and test depolarizations were preceded by short prepulses to −40 mV. Investigation of the time and voltage properties of the outward K+ transient indicated that it was inwardly rectifying and unlikely to be carried by voltage-gated channels. The outward transient was attenuated in myocytes dialyzed with high-Mg2+ solution, accelerated in myocytes dialyzed with 100 μM spermine solution, and abolished with time in myocytes dialyzed with ATP-free solution. These and other findings suggest that the outward transient is a component of classic “time-independent” inwardly rectifying K+ current.

Two electrophysiologically distinct types of cultured pacemaker cells from rabbit sinoatrial node

1986 ◽  
Vol 250 (2) ◽  
pp. H325-H329 ◽  
Author(s):  
R. D. Nathan
Keyword(s):  
Sinoatrial Node ◽  
Sodium Current ◽  
Outward Current ◽  
Slow Inward Current ◽  
Transient Outward Current ◽  
Type I ◽  
Pacemaker Cells ◽  
Inward Current ◽  
Fast Transient

Previous investigations employing multicellular nodal preparations (i.e., mixtures of dominant and subsidiary pacemaker cells) have suggested that the fast transient inward sodium current (iNa) either is not present in dominant pacemaker cells or is present but inactivated at the depolarized take-off potentials that these cells exhibit. In the present study, this question was resolved by voltage clamp analysis of single pacemaker cells isolated from the sinoatrial node and maintained in vitro for 1-3 days. Two types of cells, each with a different morphology, exhibited two modes of electrophysiological behavior. Type I cells (presumably dominant pacemakers) displayed only a tetrodotoxin (TTX)-resistant (but cadmium-sensitive) slow inward current, whereas type II cells (presumably subsidiary pacemakers) exhibited two components of inward current, a TTX-sensitive, fast transient inward current and a TTX-resistant (but cadmium-sensitive) slow inward current. Three other voltage-gated currents, 1) a slowly developing inward current activated by hyperpolarization (if, ih, delta ip), 2) a transient outward current activated by strong depolarization (ito, iA), and 3) a delayed outward current, were recorded in both types of pacemaker cells.

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