Effect of Temperature on Electrical Resonance in Leopard Frog Saccular Hair Cells

1998 ◽  
Vol 79 (1) ◽  
pp. 312-321 ◽  
Author(s):  
M. S. Smotherman ◽  
P. M. Narins
Keyword(s):  
Steady State ◽  
Resonant Frequency ◽  
Hair Cells ◽  
Outward Current ◽  
Leopard Frog ◽  
Effect Of Temperature ◽  
Channel Kinetics ◽  
Resonant Frequencies ◽  
Voltage Dependent ◽  
Electrical Resonance

Smotherman, M. S. and P. M. Narins. Effect of temperature on electrical resonance in leopard frog saccular hair cells. J. Neurophysiol. 79: 312–321, 1998. Leopard frog saccular hair cells exhibit an electrical resonance in response to a depolarizing stimulus that has been proposed to contribute to the tuning properties of the frog sacculus by acting as an electrical band-pass filter. With the whole cell patch-clamp technique, we have investigated the effect of temperature on electrical resonances in isolated saccular hair cells, and we have described the effects of temperature on the currents and channel kinetics underlying electrical resonance. A hair cell's onset resonant frequency in response to a constant depolarizing current pulse increases linearly with temperature at a rate of 11 Hz/1°C, exhibiting a mean Q 10 of 1.7 between 15 and 35°C. However, offset resonant frequencies continue to double every 10°C, exhibiting a mean Q 10 of 2.1. If steady-state voltage during the stimulus is held constant, all oscillatory frequencies increase with a mean Q 10 of 2.1. The average level of steady-state depolarization during a +150-pA depolarizing current pulse decreases with increasing temperature (−6 mV from 15 to 25°C). This temperature-dependent reduction of the steady-state membrane potential causes a shift in the voltage-dependent channel kinetics to slower rates, thus reducing the apparent Q 10 for onset resonant frequencies. The peak outward tail current and net steady-state outward current, which is the sum of a voltage-dependent inward calcium current ( I Ca) and an outward calcium-dependent potassium current ( I K(Ca)), increase with temperature, exhibiting a mean Q 10 of 1.7 between 15 and 25°C. The activation rate ( T 1/2) of the outward current exhibits a mean Q 10 of 2.3 between 15 and 25°C, while the deactivation rate (τrel) exhibits a mean Q 10 of 2.9 over the same temperature range. These results support previous models of the molecular determination of resonant frequency, which have proposed that a combination of I K(Ca) channel kinetics and the overall magnitude of the outward current are primarily responsible for determining the resonant frequency of an isolated hair cell. The robust temperature sensitivity of the hair cell receptor potential contrasts sharply with the temperature-insensitive tuning properties of in vivo saccular nerve fiber recordings. Possible explanations for this discrepancy are discussed.

Ca-Induced K+-Outward Current in Paramecium Tetraurelia

1980 ◽  
Vol 88 (1) ◽  
pp. 293-304 ◽  
Author(s):  
YOUKO SATOW ◽  
CHING KUNG
Keyword(s):  
Steady State ◽  
Voltage Clamp ◽  
Outward Current ◽  
Paramecium Tetraurelia ◽  
Ca Channels ◽  
Outward Currents ◽  
Ciliary Reversal ◽  
Voltage Dependent ◽  
K Current ◽  
K Outward Current

Late K-outward currents upon membrane depolarization were recorded in Paramecium tetraurelia under a voltage clamp. A Ca-induced K-outward component is demonstrated by subtracting the value of the outward current in a pawn A mutant lacking functional Ca-channels (pwA500). The Ca-induced K-outward current activates slowly, reaching a peak after 100 to 1000 ms. The current then remains steady or reaches the steady state after a decline of several seconds. EGTA2- injection experiments show that the Ca-induced K-outward current is dependent on the internal Ca2+ concentration. The current is shown to depend on the voltage-dependent Ca conductance, by study of the leaky pawn A mutant (pwA132), which has a lowered Ca conductance as well as a lowered Ca-induced K-current. The Ca-induced GK is thus indirectly dependent on the voltage. The maximal GK is about 40 nmho/cell at + 7 mV in 4 mM-K+. The Ca-induced K current is sustained throughout the prolonged depolarization and the prolonged ciliary reversal.

Voltage-clamp analysis of the ionic conductances in a leech neuron with a purely calcium-dependent action potential

1987 ◽  
Vol 58 (6) ◽  
pp. 1468-1484 ◽  
Author(s):  
J. Johansen ◽  
J. Yang ◽  
A. L. Kleinhaus
Keyword(s):  
Steady State ◽  
Action Potential ◽  
Time Course ◽  
Outward Current ◽  
Time Constants ◽  
Exponential Time ◽  
Calcium Dependent ◽  
Voltage Dependent ◽  
Ca Currents ◽  
Single Exponential

1. The purely calcium-dependent action potential of the anterior lateral giant (ALG) cell in the leech Haementeria was examined under voltage clamp. 2. Analysis with ion substitutions showed that the ALG cell action potential is generated by only two time- and voltage-dependent conductance systems, an inward Ca-dependent current (ICa) and an outward Ca-dependent K current IK(Ca). 3. The kinetic properties of the inward current were examined both in Cs-loaded neurons with Ca as the current carrier as well as in Ba-containing Ringer solutions with Ba as the current carrier, since Ba effectively blocked all time- and voltage-dependent outward current. 4. During a maintained depolarization, Ba and Ca currents activated with a time constant tau m, they then inactivated with the decay following a single exponential time course with a time constant tau h. The time constants for decay of both Ba and Ca currents were comparable, suggesting that the mechanism of inactivation of ICa in the ALG cell is largely voltage dependent. In the range of potentials from 5 to 45 mV, tau m varied from 8 to 2 ms and tau h varied from 250 to 125 ms. 5. The activation of currents carried by Ba, after correction for inactivation, could be described reasonably well by the expression I'Ba = I'Ba(infinity) [1--exp(-t/tau m)]. 6. The steady-state activation of the Ba-conductance mBa(infinity) increased sigmoidally with voltage and was approximated by the equation mBa(infinity) = (1 + exp[(Vh-6)/3])-1. The steady-state inactivation hBa(infinity) varied with holding potential and could be described by the equation hBa(infinity) = [1 + exp(Vh + 10/7)]-1. Recovery from inactivation of IBa was best described by the sum of two exponential time courses with time constants of 300 ms and 1.75 s, respectively. 7. The outward current IK(Ca) developed very slowly (0.5–1 s to half-maximal amplitude) and did not inactivate during a 20-s depolarizing command pulse. Tail current decay of IK(Ca) followed a single exponential time course with voltage-dependent time constants of between 360 and 960 ms. The steady-state activation n infinity of IK(Ca) increased sigmoidally with depolarization as described by the equation n infinity = [1 + exp(Vh-13.5)/-8)]-1. 8. The reversal potentials of IK(Ca) tail currents were close to the expected equilibrium potential for potassium and they varied linearly with log [K]o with a slope of 51 mV. These results suggest a high selectivity of the conductance for K ions.(ABSTRACT TRUNCATED AT 400 WORDS)

Effects of sevoflurane on inward rectifier K+ current in guinea pig ventricular cardiomyocytes

1997 ◽  
Vol 273 (1) ◽  
pp. H324-H332 ◽  
Author(s):  
A. Stadnicka ◽  
Z. J. Bosnjak ◽  
J. P. Kampine ◽  
W. M. Kwok
Keyword(s):  
Steady State ◽  
Guinea Pig ◽  
Outward Current ◽  
Inward Rectifier ◽  
Equilibrium Potential ◽  
Ventricular Cardiomyocytes ◽  
Steady State Current ◽  
Voltage Dependent ◽  
Current Activation ◽  
Extracellular Side

The effects of sevoflurane on the inward rectifier potassium current (IKIR) were examined in guinea pig ventricular cardiomyocytes using the whole cell patch-clamp methodology. Sevoflurane had a unique dual effect on the steady-state current amplitude, producing a reversible, concentration- and voltage-dependent block of the inward current at potentials negative to the potassium equilibrium potential (EK) but enhancing the outward current positive to EK. Accordingly, the steady-state conductance negative to EK was reduced by sevoflurane, but conductance positive to EK was increased. The chord conductance-voltage relationship showed depolarizing shifts at 0.7, 1.3, and 1.6 mM sevoflurane. When the myocytes were dialyzed with 10 mM Mg2+, but not with 1.0 mM Mg2+, sevoflurane further slowed current activation kinetics. With 10 mM intracellular Mg2+, the outward current enhancement by sevoflurane and the associated shifts in half-activation potential were abolished. Polyamines abolished all effects of sevoflurane on IKIR. With the use of the Woodhull model for voltage-dependent block, we determined the sevoflurane interaction site with the inward rectifier potassium channel to be at an electrical distance of 0.2 from the extracellular side.

scholarly journals The calcium-activated potassium channels of turtle hair cells.

1995 ◽  
Vol 105 (1) ◽  
pp. 49-72 ◽  
Author(s):  
J J Art ◽  
Y C Wu ◽  
R Fettiplace
Keyword(s):  
Resonant Frequency ◽  
Time Constant ◽  
Hair Cells ◽  
Time Course ◽  
Voltage Dependence ◽  
Bk Channels ◽  
Hair Bundle ◽  
Sk Channels ◽  
Channel Kinetics ◽  
Ca Current

A major factor determining the electrical resonant frequency of turtle cochlear hair cells is the time course of the Ca-activated K current (Art, J. J., and R. Fettiplace. 1987. Journal of Physiology. 385:207-242). We have examined the notion that this time course is dictated by the K channel kinetics by recording single Ca-activated K channels in inside-out patches from isolated cells. A hair cell's resonant frequency was estimated from its known correlation with the dimensions of the hair bundle. All cells possess BK channels with a similar unit conductance of approximately 320 pS but with different mean open times of 0.25-12 ms. The time constant of relaxation of the average single-channel current at -50 mV in 4 microM Ca varied between cells from 0.4 to 13 ms and was correlated with the hair bundle height. The magnitude and voltage dependence of the time constant agree with the expected behavior of the macroscopic K(Ca) current, whose speed may thus be limited by the channel kinetics. All BK channels had similar sensitivities to Ca which produced half-maximal activation for a concentration of approximately 2 microM at +50 mV and 12 microM at -50 mV. We estimate from the voltage dependence of the whole-cell K(Ca) current that the BK channels may be fully activated at -35 mV by a rise in intracellular Ca to 50 microM. BK channels were occasionally observed to switch between slow and fast gating modes which raises the possibility that the range of kinetics of BK channels observed in different hair cells reflects a common channel protein whose kinetics are regulated by an unidentified intracellular factor. Membrane patches also contained 30 pS SK channels which were approximately 5 times more Ca-sensitive than BK channels at -50 mV. The SK channels may underlie the inhibitory synaptic potential produced in hair cells by efferent stimulation.

Transfer impedances between different regions of branched excitable cells

1988 ◽  
Vol 59 (3) ◽  
pp. 689-705 ◽  
Author(s):  
L. E. Moore ◽  
K. Yoshii ◽  
B. N. Christensen
Keyword(s):  
Resonant Frequency ◽  
Voltage Clamp ◽  
Growth Cone ◽  
Transfer Functions ◽  
Excitable Cells ◽  
Resonant Frequencies ◽  
Steady State Current ◽  
Branching Patterns ◽  
Voltage Dependent ◽  
Impedance Functions

1. The excitable properties of branched cells were measured using a combination of voltage-clamp and frequency-domain techniques. Point impedance functions from either the soma or growth cone of NG-108 cells were curve fitted with a reduced cable model at different membrane potentials to establish kinetic parameters. 2. Transfer impedance functions between the soma and growth cone were measured and simulated with a morphologically determined model. In these experiments the membrane potential was controlled by a single-electrode voltage clamp thus allowing an estimate of transfer functions for any arbitrary input, such as a single synaptic current for differing degrees of tonic synaptic drive. Furthermore, the integration of different regional inputs was evaluated based on the transfer functions between different locations on an individual cell. 3. The activation of an outward steady-state current leads to resonating impedance functions that were used to evaluate the kinetic properties of ionic channels in different regions of branched excitable cells. For simple branching patterns the point and transfer impedances show lower resonant frequencies for active growth cones compared with active somas. 4. More complex branching patterns showed the unexpected result that the voltage-dependent resonant frequency was higher for the growth cone recording than the soma. The presence of a higher resonant frequency when the growth cone is activated does not require more rapid kinetics of the active potassium conductance, since the time constant of the active conductance can be the same in the growth cone and the soma membrane. 5. In conclusion, the resonant frequencies, as well as all other aspects of the impedance functions, are complicated interactions of the detailed branching patterns and active conductances. In general, these interactions are not predictable from a passive electrotonic analysis, especially when the voltage-dependent conductances are distributed throughout the dendritic tree.

The inactivating potassium currents of hair cells isolated from the crista ampullaris of the frog

1992 ◽  
Vol 68 (5) ◽  
pp. 1642-1653 ◽  
Author(s):  
C. H. Norris ◽  
A. J. Ricci ◽  
G. D. Housley ◽  
P. S. Guth
Keyword(s):  
Steady State ◽  
Hair Cells ◽  
Reversal Potential ◽  
Semicircular Canals ◽  
Cell Voltage ◽  
Leopard Frog ◽  
Resting Potential ◽  
Voltage Response ◽  
Calcium Dependent ◽  
Steady State Inactivation

1. A-type outward currents were studied in sensory hair cells isolated from the semicircular canals (SCC) of the leopard frog (Rana pipiens) with whole-cell voltage- and current-clamping techniques. 2. There appear to be two classes of A-type outward-conducting potassium channels based on steady-state, kinetic, pharmacological parameters, and reversal potential. 3. The two classes of A-type currents differ in their steady-state inactivation properties as well as in the kinetics of inactivation. The steady-state inactivation properties are such that a significant portion of the fast channels are available from near the resting potential. 4. The inactivating channels studied do not appear to be calcium dependent. 5. The A-channels in hair cells appear to subserve functions that are analogous to IA functions in neurons, that is, modulating spike latency and Q (the oscillatory damping function). The A-currents appear to temporally limit the hair cell voltage response to a current injection.

Voltage-dependent block by neomycin of the ATP-induced whole cell current of guinea-pig outer hair cells

1993 ◽  
Vol 70 (4) ◽  
pp. 1593-1605 ◽  
Author(s):  
X. Lin ◽  
R. I. Hume ◽  
A. L. Nuttall
Keyword(s):  
Steady State ◽  
Guinea Pig ◽  
Hair Cells ◽  
Time Course ◽  
Outer Hair Cells ◽  
Current Noise ◽  
Whole Cell ◽  
Voltage Dependent ◽  
Cell Current ◽  
Whole Cell Current

1. The effects of externally applied ATP and neomycin on whole cell currents of isolated guinea pig cochlear outer hair cells (OHCs) were studied using the whole cell voltage-clamp technique. In OCHs held at -70 mV, ATP activated a large inward current. In the presence of neomycin, the ATP-induced whole cell current activated along a relatively unaltered time course, but the current then decreased to a reduced steady level. The neomycin inhibition of the ATP-induced current was dose dependent. The half-inhibitory concentration (IC50) of neomycin measured at steady state was estimated to be 90 microM. 2. Neomycin inhibition of the ATP response could not be reversed by increasing the concentration of ATP, indicating that the effect was noncompetitive. The inhibition was voltage dependent and was greatly reduced when OHCs were held at positive potentials. 3. Cells treated with 100 microM ATP gave maximal current responses. Addition of neomycin substantially increased membrane current noise of the 100 microM ATP responses. When neomycin concentration was varied from 10 to 500 microM, the current noise level peaked between 50 and 100 microM. The noise increase was observed at negative holding potentials but not at positive potentials. 4. The neomycin-induced whole cell current noise was used to estimate the size of the underlying elementary current. The ATP-induced single channel current of OHCs at -70 mV was estimated to be approximately 0.3 pA. The number of ATP-activated channels in a single OHC was estimated to be in the range of a few thousand. 5. The characteristics of the neomycin inhibition of ATP-induced currents were consistent with an open channel blocking mechanism. Analysis of the voltage dependence of the steady state neomycin inhibition suggested a neomycin binding site at an electrical distance of 0.3 from the extracellular side.

Studies of solitary semicircular canal hair cells in the adult pigeon. II. Voltage-dependent ionic conductances

1989 ◽  
Vol 62 (4) ◽  
pp. 935-945 ◽  
Author(s):  
D. G. Lang ◽  
M. J. Correia
Keyword(s):  
Hair Cells ◽  
Semicircular Canal ◽  
Potassium Conductance ◽  
Outward Current ◽  
Resting Membrane Potential ◽  
Calcium Dependent ◽  
Ionic Conductances ◽  
Voltage Dependent ◽  
Steady State Inactivation ◽  
Inward Currents

1. The ionic conductances present in putative type II hair cells enzymatically dissociated from the anterior, posterior, and lateral semicircular canal cristae of the white king pigeon (Columba livia) vestibule were studied under whole cell voltage clamp. 2. Two classes of voltage-dependent potassium conductances were distinguishable on the basis of the time course of activation and inactivation and pharmacologic sensitivity. The rapid potassium conductance, IA, as inhibited by 6 mM 4-aminopyridine (4-AP), whereas the slow potassium conductance, IK, was inhibited by 50 mM tetraethylammonium (TEA). These conductances were not affected by extracellular calcium removal. IA was quite similar to the rapidly-inactivating A-current of molluscan soma, whereas IK was more like the delayed rectifier of molluscan soma. 3. The steady-state inactivation of IA occurred over a potential range from -100 to -40 mV. The threshold for activation of IA occurred between -60 and -50 mV. The slope conductance of the I-V curve over a range of -50 to -20 mV was 13.7 nS when the conditioning pulse was -100 mV, and we estimate it to be approximately 1-2 nS from the resting membrane potential of -56 mV. 4. The steady-state inactivation of IK was approximately 60% at -40 mV and was completely removed at -80 mV. The threshold for activation of IK was between -50 and -40 mV. The slope conductance of the I-V curve over a range of -50 to -20 mV was 10.5 nS when the conditioning pulse was -80 mV, and we estimate it to be approximately 6-7 nS from the resting potential of -56 mV. 5. At -56 mV (the average resting membrane potential of putative type II semicircular canal hair cells), approximately 10-14% of IA channels and approximately 57-70% of IK channels were not inactivated: thus IA and IK can contribute to the outward current during small depolarizations from rest. 6. A small calcium-dependent outward current, IK(Ca), could be elicited during step depolarizations from a holding potential of -40 mV. This calcium-dependent current was active over the range of -20 to +40 mV. 7. Inward currents could not be detected when the cells were exposed to normal physiological solutions. However, when the outward currents were blocked with internal cesium and the external solution contained 20 mM barium, sustained inward currents with rapid activation kinetics could be detected. The threshold for activation of the inward current occurred at -40 mV, and the I-V relationship peaked at -10 mV.(ABSTRACT TRUNCATED AT 400 WORDS)

scholarly journals Modification of potassium channel kinetics by histidine-specific reagents.

1990 ◽  
Vol 96 (4) ◽  
pp. 757-775 ◽  
Author(s):  
S Spires ◽  
T Begenisich
Keyword(s):  
Steady State ◽  
Potassium Channels ◽  
Potassium Channel ◽  
Conformational Transition ◽  
Dependent Manner ◽  
Channel Kinetics ◽  
Gating Currents ◽  
External Application ◽  
Steady State Current ◽  
Voltage Dependent

We have examined the actions of histidine-specific reagents on potassium channels in squid giant axons. External application of 20-500 microM diethylpyrocarbonate (DEP) slowed the opening of potassium channels with little or no effect on closing rates. Sodium channels were not affected by these low external concentrations of DEP. Internal application of up to 2 mM DEP had no effect on potassium channel kinetics. Steady-state potassium channel currents were reduced in an apparently voltage-dependent manner by external treatment with this reagent. The shape of the instantaneous current-voltage relation was not altered. The voltage-dependent probability of channel opening was shifted toward more positive membrane potentials, thus accounting for the apparent voltage-dependent reduction of steady-state current. Histidine-specific photo-oxidation catalyzed by rose bengal produced alterations in potassium channel properties similar to those observed with DEP. The rate of action of DEP was consistent with a single kinetic class of histidine residues. In contrast to the effects on ionic currents, potassium channel gating currents were not modified by treatment with DEP. These results suggest the existence of a histidyl group (or groups) on the external surface of potassium channels important for a weakly voltage-dependent conformational transition. These effects can be reproduced by a simple kinetic model of potassium channels.

scholarly journals Serotonin differentially modulates two K+ currents in the Retzius cell of the leech

1989 ◽  
Vol 145 (1) ◽  
pp. 403-417
Author(s):  
J. Acosta-Urquidi ◽  
C. L. Sahley ◽  
A. L. Kleinhaus
Keyword(s):  
Steady State ◽  
Action Potential ◽  
Voltage Clamp ◽  
Negative Feedback ◽  
Outward Current ◽  
Current Clamp ◽  
Macrobdella Decora ◽  
Voltage Dependent ◽  
Retzius Cell ◽  
K Currents

The effects of 100 mumol l-1 serotonin (5-HT) were investigated on the Na+- and Ca2+-dependent action potential and distinct K+ currents in the Retzius (R) cells of the hirudinid leeches Macrobdella decora and Hirudo medicinalis by conventional current-clamp and two-microelectrode voltage-clamp techniques. 1. In normal Na+-containing Ringer, 5-HT decreased the duration of the action potential prolonged by 5 mmol l-1 tetraethylammonium (TEA+) chloride. 2. In Na+-free saline containing 25 mumol l-1 TEA+ to block IK, 5-HT reduced the amplitude and duration of Ca2+ spikes evoked by intracellular current injection. 3. Under voltage-clamp, 5-HT enhanced the peak amplitude of an early transient 4-aminopyridine (4-AP)-sensitive, voltage-dependent outward current, termed IA. A small but significant increase in the time constant of inactivation (tau off) of IA was also measured after exposure to 5-HT. 4. 5-HT suppressed the peak and steady-state amplitudes of a delayed TEA+-sensitive, voltage-dependent outward current, termed IK. These results demonstrate differential simultaneous modulation of distinct K+ currents in the Retzius cell of the leech by the endogenous transmitter serotonin. These cells contain and release 5-HT, and are believed to be multifunction neurons implicated in feeding and swimming. This modulation may change the excitable properties of the cell, leading to a negative feedback autoregulation of its transmitter output.

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