Triiodothyronine affects the electrical properties of GH3 cells

1990 ◽  
Vol 123 (1) ◽  
pp. 51-60 ◽  
Author(s):  
John S. du Pont
Keyword(s):  
Membrane Potential ◽  
Electrical Properties ◽  
Action Potentials ◽  
Channel Blocker ◽  
Membrane Resistance ◽  
Gh3 Cells ◽  
Current Clamp ◽  
Potential Capacity ◽  
Rat Pituitary ◽  
A Current

Abstract. Electrophysiological experiments show that T3 has a direct effect on the cell membrane of GH3 cells, a transformed line from the rat pituitary. Slope conductance versus membrane potential, resting membrane resistance, potential, capacity and action potentials were measured in this study. Using a current clamp technique, the effects of tetrodotoxin, tetraethylammonium, apamin, and nifedipine were measured and compared with those directly evoked by T3. T3 increased the slope conductance: 1. at around −60 mV, as did tetrodotoxin (Na+ channel blocker); 2. at about −40 mV, as did nifedipine (Ca2+ channel blocker), but decreased this conductance strongly between −20 and −30 mV, as did both nifedipine and apamin (Ca2+-sensitive K+ channel blocker). Action potentials were inhibited by T3 and by nifedipine. Action potentials in these cells are primarily related to Ca2+ ions. It seems that T3 inhibits the Ca2+ current and, as a consequence, the Ca2+-sensitive K+ current.

scholarly journals Ca2+-activated Cl− current in sheep lymphatic smooth muscle

2000 ◽  
Vol 279 (5) ◽  
pp. C1327-C1335 ◽  
Author(s):  
H. M. Toland ◽  
K. D. McCloskey ◽  
K. D. Thornbury ◽  
N. G. McHale ◽  
M. A. Hollywood
Keyword(s):  
Smooth Muscle ◽  
Carboxylic Acid ◽  
Patch Clamp ◽  
Action Potentials ◽  
Channel Blocker ◽  
Equilibrium Potential ◽  
Plateau Phase ◽  
Current Clamp ◽  
Patch Clamp Technique ◽  
Perforated Patch Clamp

Freshly dispersed sheep mesenteric lymphatic smooth muscle cells were studied at 37°C using the perforated patch-clamp technique with Cs+- and K+-filled pipettes. Depolarizing steps evoked currents that consisted ofl-type Ca2+ [ I Ca(L)] current and a slowly developing current. The slow current reversed at 1 ± 1.5 mV with symmetrical Cl− concentrations compared with 23.2 ± 1.2 mV ( n = 5) and −34.3 ± 3.5 mV ( n = 4) when external Cl− was substituted with either glutamate (86 mM) or I− (125 mM). Nifedipine (1 μM) blocked and BAY K 8644 enhanced I Ca(L), the slow-developing sustained current, and the tail current. The Cl− channel blocker anthracene-9-carboxylic acid (9-AC) reduced only the slowly developing inward and tail currents. Application of caffeine (10 mM) to voltage-clamped cells evoked currents that reversed close to the Cl− equilibrium potential and were sensitive to 9-AC. Small spontaneous transient depolarizations and larger action potentials were observed in current clamp, and these were blocked by 9-AC. Evoked action potentials were triphasic and had a prominent plateau phase that was selectively blocked by 9-AC. Similarly, fluid output was reduced by 9-AC in doubly cannulated segments of spontaneously pumping sheep lymphatics, suggesting that the Ca2+-activated Cl− current plays an important role in the electrical activity underlying spontaneous activity in this tissue.

Input Resistance, Time Constants, and Spike Initiation

1998 ◽  
Author(s):  
Christof Koch
Keyword(s):  
Membrane Potential ◽  
Time Constant ◽  
Action Potentials ◽  
Input Resistance ◽  
Current Injection ◽  
Membrane Conductances ◽  
Voltage Dependent ◽  
Dc Component ◽  
Definition Of ◽  
A Current

This chapter represents somewhat of a tephnical interlude. Having introduced the reader to both simplified and more complex compartmental single neuron models, we need to revisit terrain with which we are already somewhat familiar. In the following pages we reevaluate two important concepts we defined in the first few chapters: the somatic input resistance and the neuronal time constant. For passive systems, both are simple enough variables: Rin is the change in somatic membrane potential in response to a small sustained current injection divided by the amplitude of the current injection, while τm is the slowest time constant associated with the exponential charging or discharging of the neuronal membrane in response to a current pulse or step. However, because neurons express nonstationary and nonlinear membrane conductances, the measurement and interpretation of these two variables in active structures is not as straightforward as before. Having obtained a more sophisticated understanding of these issues, we will turn toward the question of the existence of a current, voltage, or charge threshold at which a biophysical faithful model of a cell triggers action potentials. We conclude with recent work that suggests how concepts from the subthreshold domain, like the input resistance or the average membrane potential, could be extended to the case in which the cell is discharging a stream of action potentials. This chapter is mainly for the cognoscendi or for those of us that need to make sense of experimental data by comparing therp to theoretical models that usually fail to reflect reality adequately. In Sec. 3.4, we defined Kii (f) for passive cable structures as the voltage change at location i in response to a sinusoidal current injection of frequency f at the same location. Its dc component is also referred to as input resistance or Rin. Three difficulties render this definition of input resistance problematic in real cells: (1) most membranes, in particular at the soma, show voltage-dependent nonlinearities, (2) the associated ionic membrane conductances are time dependent and (3) instrumental aspects, such as the effect of the impedance of the recording electrode on Rin, add uncertainty to the measuring process.

scholarly journals The Effect of Aconitine on the Giant Axon of the Squid

1964 ◽  
Vol 47 (4) ◽  
pp. 719-733 ◽  
Author(s):  
W. H. Herzog ◽  
R. M. Feibel ◽  
S. H. Bryant
Keyword(s):  
Membrane Potential ◽  
Action Potential ◽  
Action Potentials ◽  
Giant Axon ◽  
Membrane Resistance ◽  
Repetitive Stimulation ◽  
Resting Membrane Potential ◽  
Sustained Activity ◽  
Frequency Of Stimulation ◽  
Sodium And Potassium

In the giant axon of Loligo pealii, "aconitine potent" Merck added to the bath (10-7 to 1.25 x 10-6 gm/ml) (a) had no effect on resting membrane potential, membrane resistance and rectification, membrane response to subthreshold currents, critical depolarization, or action potential, but (b) on repetitive stimulation produced oscillations of membrane potential after the spike, depolarization, and decrease of membrane resistance. The effect sums with successive action potentials; it increases with concentration of aconitine, time of exposure, and frequency of stimulation. When the oscillations are large enough and the membrane potential is 51.6 ± SD 1.5 mv a burst of self-sustained activity begins; it usually lasts 20 to 70 sec. and at its end the membrane potential is 41.5 ± SD 1.9 mv. Repolarization occurs with a time constant of 2.5 to 11.1 min. Substitution of choline for external sodium after a burst hyperpolarizes the membrane to -70 mv, and return to normal external sodium depolarizes again beyond the resting membrane potential. The effect of aconitine on the membrane is attributed to an increase of sodium and potassium or chloride conductances following the action potential.

scholarly journals Electrophysiology of the Heart of an Isopod Crustacean: Porcellio Dilatatus

1972 ◽  
Vol 57 (3) ◽  
pp. 609-631
Author(s):  
J. C. DELALEU ◽  
A. BLONDEAU ◽  
A. HOLLEY
Keyword(s):  
Membrane Potential ◽  
Action Potentials ◽  
Additional Data ◽  
Ionic Currents ◽  
Membrane Resistance ◽  
Resting Membrane Potential ◽  
Plateau Phase ◽  
Bathing Medium ◽  
Ionic Conductances ◽  
Rate Of Decline

1. The effects of various ions and chemicals were tested on the resting or active membrane of the heart of the wood-louse Porcellio dilatatus. 2. The curve relating the resting membrane potential to log [K+]o was found to correspond with the theoretical curve expected from the Nernst equation at higher concentrations only. Excess K+ decreased both amplitude and rate of rise of the response while the rate of decline was increased. In K+-deficient solutions the duration of the plateau phase was at first increased, then depressed. The addition of K+ to a bathing medium deprived for several minutes of this ion caused a large increase in the membrane potential and in the response height. The way in which the membrane was seen to react was tentatively attributed to an electrogenic active pumping mechanism. 3. In Na+-deficient solutions, the rate of rise and the height of the response were reduced while the resting membrane potential was decreased. 4. Ca2+-deficient solutions depolarized the membrane and decreased both amplitude and duration of the response. Cessation of activity occurred in Ca2+-free solution. In excess calcium the membrane was hyperpolarized. The rhythm and the rate of rising were decreased and the plateau phase depressed. 5. TTX blocked the heart activity, probably by acting upon the heart ganglion. Mn2+ depressed especially the humped plateau (when present) of the spontaneous responses. 6. TEA, caffeine and procaine transformed spontaneous activity of weak amplitude into large and complex overshooting responses. In TEA solutions, several stable levels of polarization were observed. Contrary to what occurred in the normal solution, depolarizing current pulses could trigger large all-or-none action potentials when TEA was present. 7. The TEA-induced regenerative response was analysed with the help of an intracellular stimulating current when [Na+]o and [Ca2+]o were varied. Additional data were obtained by applying TTX, Mn2+ or GABA. From the results, both Ca2+ and Na+ were thought to be involved in the ionic currents underlying spike type activity. 8. The spike-generating effect of TEA has been attributed to its property of increasing the membrane resistance and of allowing the ionic conductances which generate the weakly active component of the normal response, the plateau, but not the initial upstroke, to be amplified regeneratively. 9. The large spikes elicited by TEA were found relatively less effective than weak sustained depolarization in inducing strong contractions. 10. The functional significance of the data was tentatively interpreted by comparison with the properties of the heart of Limulus, Crustacea and vertebrates.

Electrical properties of neurons recorded from the rat supraoptic nucleus in vitro

1983 ◽  
Vol 217 (1207) ◽  
pp. 141-161 ◽  
Keyword(s):  
Membrane Potential ◽  
Electrical Properties ◽  
Time Constant ◽  
Synaptic Input ◽  
Action Potentials ◽  
Supraoptic Nucleus ◽  
Synaptic Activity ◽  
Intracellular Recordings ◽  
Average Cell ◽  
Spike Threshold

The electrical properties of neurons in the supraoptic nucleus (so.n.) have been studied in the hypothalamic slice preparation by intracellular and extracellular recording techniques, with Lucifer Yellow CH dye injection to mark the recording site as being the so. n. Intracellular recordings from so. n. neurons revealed them to have an average membrane potential of ─ 67±0.8 mV (mean±s. e. m.), membrane resistance of 145±9 MΩ with linear current–voltage relations from 40 mV in the hyperpolarizing direction to the level of spike threshold in the depolarizing direction. Average cell time constant was 14±2.2 ms. So. n. action potentials ranged in amplitude from 55 to 95 mV, with a mean of 76±2 mV, and a spike width of 2.6±0.5 ms at 30% of maximal spike height. Both single spikes and trains of spikes were followed by a strong, long-lasting hyperpolarization with a decay fitted by a single exponential having a time constant of 8.6±1.8 ms. Action potentials could be blocked by 10 -6 m tetrodotoxin. Spontaneously active so. n. neurons were characterized by synaptic input in the form of excitatory and inhibitory postsynaptic potentials, the latter being apparently blocked when 4 m KCI electrodes were used. Both forms of synaptic activity were blocked by application of divalent cations such as Mg 2+ , Mn 2+ or Co 2+ . 74% of so. n. neurons fired spontaneously at rates exceeding 0.1 spikes per second, with a mean for all cells of 2.9±0.2 s -1 . Of these cells, 21% fired slowly and continuously at 0.1─1.0 s -1 , 45 % fired continuously at greater than 1 Hz, and the remaining 34% fired phasically in bursts of activity followed by silence or low frequency firing. Spontaneously firing phasic cells showed a mean burst length of 16.7± 4.5 s and a silent period of 28.2±4.2 s. Intracellular recordings revealed the presence of slow variations in membrane potential which modified the neuron’s proximity to spike threshold, and controlled phasic firing. Variations in synaptic input were not observed to influence firing in phasic cells.

scholarly journals T-type Ca2+ channel lowers the threshold of spike generation in the newt olfactory receptor cell.

1996 ◽  
Vol 108 (6) ◽  
pp. 525-535 ◽  
Author(s):  
F Kawai ◽  
T Kurahashi ◽  
A Kaneko
Keyword(s):  
Action Potential ◽  
Olfactory Receptor ◽  
Action Potentials ◽  
Channel Blocker ◽  
Receptor Cell ◽  
Spike Generation ◽  
Current Clamp ◽  
Patch Clamp Technique ◽  
Olfactory Receptor Cell ◽  
Clamp Condition

Mechanisms underlying action potential generation in the newt olfactory receptor cell were investigated by using the whole-cell version of the patch-clamp technique. Isolated olfactory cells had a resting membrane potential of -70 +/- 9 mV. Injection of a depolarizing current step triggered action potentials under current clamp condition. The amplitude of the action potential was reduced by lowering external Na+ concentration. After a complete removal of Na+, however, cells still showed action potentials which was abolished either by Ca2+ removal or by an application of Ca2+ channel blocker (Co2+ or Ni2+), indicating an involvement of Ca2+ current in spike generation of newt olfactory receptor cells. Under the voltage clamp condition, depolarization of the cell to -40 mV from the holding voltage of -100 mV induced a fast transient inward current, which consisted of Na+ (INa) and T-type Ca2+ (ICa.T) currents. The amplitude of ICa,T was about one fourth of that of INa. Depolarization to more positive voltages also induced L-type Ca2+ current (ICa,L). ICa,L was as small as a few pA in normal Ringer solution. The activating voltage of ICa,T was approximately 10 mV more negative than that of INa. Under current clamp, action potentials generated by a least effective depolarization was almost completely blocked by 0.1 mM Ni2+ (a specific T-type Ca2+ channel blocker) even in the presence of Na+. These results suggest that ICa,T contributes to action potential in the newt olfactory receptor cell and lowers the threshold of spike generation.

Pharmacological characterization of two calcium currents in GH3 cells

1988 ◽  
Vol 254 (3) ◽  
pp. E328-E336 ◽  
Author(s):  
S. M. Simasko ◽  
G. A. Weiland ◽  
R. E. Oswald
Keyword(s):  
Channel Blocker ◽  
Pituitary Cell ◽  
Calcium Currents ◽  
Gh3 Cells ◽  
Pharmacological Properties ◽  
Pharmacological Characterization ◽  
Whole Cell Patch Clamp ◽  
Rat Pituitary ◽  
Dihydropyridine Calcium Channel Blocker

Whole cell patch-clamp techniques were used to investigate the pharmacological properties of calcium currents in the clonal rat pituitary cell line GH3. Current traces induced by a 100-ms pulse to 0 mV from a holding potential of -80 mV consisted of a component that rapidly inactivated during the pulse and a component that slowly inactivated during the pulse. When the holding potential was reduced to -32 mV, the rapidly inactivating component of the trace disappeared. The dihydropyridine calcium channel blocker nitrendipine affected only the slowly inactivating component of the trace. At a holding potential of -80 mV, nitrendipine blocked the slowly inactivating current with an IC50 of 1 microM. The IC50 for nitrendipine was found to be dependent on the holding potential, decreasing to 10 nM when the holding potential was -32 mV. The dihydropyridine agonist Bay-K 8644, like nitrendipine, affected only the slowly inactivating component. The inorganic blocker Cd2+ blocked both components but the slowly inactivating current was three- to fourfold more sensitive. These results are best explained by the existence of two types of calcium channels in these cells, one sensitive to dihydropyridines and one insensitive to dihydropyridines. These channels appear analogous to the T-type channel (inactivating current) and L-type channel (slowly inactivating current) described in other preparations.

Whole cell recording from lobster olfactory receptor cells: responses to current and odor stimulation

1989 ◽  
Vol 61 (5) ◽  
pp. 994-1000 ◽  
Author(s):  
I. Schmiedel-Jakob ◽  
P. A. Anderson ◽  
B. W. Ache
Keyword(s):  
Membrane Potential ◽  
Electrical Properties ◽  
Olfactory Receptor ◽  
Action Potentials ◽  
Receptor Potential ◽  
Membrane Potentials ◽  
Patch Clamp Recording ◽  
Whole Cell ◽  
Olfactory Receptor Cells ◽  
Receptor Cells

1. The basic electrical properties of olfactory (antennule) receptor cells were studied in an in situ preparation of the spiny lobster using whole cell patch-clamp recording. 2. The current-voltage relationship of the cells was linear for membrane potentials between -150 and -40 mV and rectified at more positive membrane potentials. The input resistance at rest averaged 508 M omega. The cells displayed two time constants, with mean values of 29.8 and 8.2 ms. 3. Depolarizing current steps elicited fast, overshooting action potentials at a mean threshold of -32 mV from an imposed resting membrane potential of -65 mV. The action potentials were tetrodotoxin (TTX) and tetraethylammonium (TEA) sensitive, suggesting they are typical sodium/potassium action potentials. 4. Odor stimulation evoked slow, dose-dependent, depolarizing receptor potentials up to 50 mV in amplitude. In approximately 30% of cells tested, these led to repetitive spiking when the cells were depolarized beyond -45 to -30 mV. The amplitude of the receptor potential was graded as a linear function of the logarithm of the odor concentration. 5. The amplitude of the receptor potential varied linearly with the membrane potential between -70 and -30 mV. Extrapolated reversal potentials appeared to be normally distributed around a mean value of -3.6 mV. 6. The results collectively indicate that lobster olfactory receptor cells have electrical properties similar to, but not necessarily identical with, those currently envisaged for olfactory receptor cells in other species.

The Modulatory Action of Dopamine on Crustacean Foregut Neuromuscular Preparations

1981 ◽  
Vol 94 (1) ◽  
pp. 285-299
Author(s):  
CHRIS LINGLE
Keyword(s):  
Electrical Properties ◽  
Muscle Contraction ◽  
Muscle Fibre ◽  
Action Potentials ◽  
Muscle Relaxation ◽  
Membrane Resistance ◽  
Membrane Potentials ◽  
Half Time ◽  
Spontaneous Contractions ◽  
Evoked Contractions

1. Effects of dopamine (DA) on contractile and electrical properties of decapod foregut neuromuscular preparations were examined. 2. Dopamine produced dramatic increases in nerve-evoked contractions and, in particular muscles, contractures and spontaneous contractions. These effects were observed at concentrations as low as 5 × 10−9M-DA. 3. The DA-produced enhancement of nerve-evoked contractions was associated with an increase in amplitude of excitatory junctional potentials (EJPs). 4. The increase in EJPs resulted in part from an increase in muscle fibre membrane resistance that was particularly prominent over depolarized membrane potentials. A presynaptic action of dopamine cannot be as yet excluded. 5. In fibres from the muscle in which dopamine produced a contracture, dopamine also produced a depolarization. 6. In fibres from the muscle in which dopamine activated spontaneous contractions, dopamine also produced spontaneous rhythmic action potentials. 7. Dopamine also accelerated the half-time of muscle relaxation following muscle contraction.

scholarly journals Passive Electrical Properties of Paramecium and Problems of Ciliary Coordination

1970 ◽  
Vol 55 (4) ◽  
pp. 467-483 ◽  
Author(s):  
Roger Eckert ◽  
Yutaka Naitoh
Keyword(s):  
Plasma Membrane ◽  
Membrane Potential ◽  
Electrical Properties ◽  
Action Potentials ◽  
Cable Model ◽  
Ciliary Reversal ◽  
Entire Cell ◽  
Passive Electrical Properties ◽  
Metachronal Waves ◽  
Ciliary Beat

Potential recordings made simultaneously from opposite ends of the cell indicate that the cytoplasmic compartment of P. caudatum is nearly isopotential. Measured decrements of the spread of steady-state potentials are in essential agreement with calculated decrements for a short cable model of similar dimensions and electrical constants. Action potentials and passively conducted pulses spread at rates of over 100 µm per msec. In contrast, metachronal waves of ciliary beat progress over the cell with velocities below 1 µm per msec. Thus, electrical activity conducted by the plasma membrane cannot account for the metachronism of ciliary beat. The electrical properties of Paramecium are responsible, however, for coordinating the reorientation of cilia (either beating or paralyzed by NiCl2) which occurs over the entire cell in response to current passed across the plasma membrane. In response to a depolarization the cilia assume an anteriorly directed orientation ("ciliary reversal" for backward locomotion). The cilia over the anterior half of the organism reverse more strongly and with shorter latency than the cilia of the posterior half. This was true regardless of the location of the polarizing electrode. Since the membrane potential was shown to be essentially uniform between both ends of the cell, the cilia of the anterior and posterior must possess different sensitivities to membrane potential.

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