Cd2+ regulation of the hyperpolarization-activated current IAB in crayfish muscle (original) (raw)
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Novel inward rectifier blocked by Cd2+ in crayfish muscle
Brain Research, 1991
The characteristics of a voltage-and time-dependent inward rectifying current were examined with voltage clamp techniques in crayfish muscle. The inward current, carried by K +, was activated by hyperpolarization. Although this inward current increased with the extracellular K ÷ concentration ([K+]o), the voltage-dependence of the underlying conductance was independent of [K+]o. The current was unaffected by Cs + and Ba 2+, but was blocked by low concentrations of Cd 2+. Therefore, this inward rectifier is different than previously described ones.
Journal of neurophysiology, 1998
Crayfish opener muscle fibers provide a unique preparation to quantitatively evaluate the relationships between the voltage-gated Ca2+ (ICa) and Ca2+-activated K+ (IK(Ca)) currents underlying the graded action potentials (GAPs) that typify these fibers. ICa, IK(Ca), and the voltage-gated K+ current (IK) were studied using two-electrode voltage-clamp applying voltage commands that simulated the GAPs evoked in current-clamp conditions by 60-ms current pulses. This methodology, unlike traditional voltage-clamp step commands, provides a description of the dynamic aspects of the interaction between different conductances participating in the generation of the natural GAP. The initial depolarizing phase of the GAP was due to activation of the ICa on depolarization above approximately -40 mV. The resulting Ca2+ inflow induced the activation of the fast IK(Ca) (<3 ms), which rapidly repolarized the fiber (<6 ms). Because of its relatively slow activation, the contribution of IK to the...
Fast BK-type channel mediates the Ca(2+)-activated K(+) current in crayfish muscle
Journal of neurophysiology, 1999
The role of the Ca(2+)-activated K(+) current (I(K(Ca))) in crayfish opener muscle fibers is functionally important because it regulates the graded electrical activity that is characteristic of these fibers. Using the cell-attached and inside-out configurations of the patch-clamp technique, we found three different classes of channels with properties that matched those expected of the three different ionic channels mediating the depolarization-activated macroscopic currents previously described (Ca(2+), K(+), and Ca(2+)-dependent K(+) currents). We investigated the properties of the ionic channels mediating the extremely fast activating and persistent I(K(Ca)). These voltage- and Ca(2+)-activated channels had a mean single-channel conductance of approximately 70 pS and showed a very fast activation. Both the single-channel open probability and the speed of activation increased with depolarization. Both parameters also increased in inside-out patches, i.e., in high Ca(2+) concentrati...
Crayfish stretch receptor: an investigation with voltage-clamp and ion-sensitive electrodes
The Journal of Physiology, 1978
1. The membrane characteristics of the slowly adapting stretch receptor from the crayfish, Asta8us fiuviatilis, were examined with electrophysiological techniques consisting of membrane potential recording, voltage clamp and ion-sensitive microelectrodes. 2. The passive membrane current (Ip) following step changes of the membrane potential to levels above 0 mV required more than a minute to decay to a steadystate level. 3. The stretch-induced current (SIC, where SIC = total-Ipassive) was not fully developed until the Ip had decayed to a steady state. 4. With Ip at the steady state and the stretch-induced current at the 0-current potential, a slow stretch-induced inward current was isolated. The latter reaches a maximum after 1 see of stretch and declines even more slowly after stretch. The I-V relation of the slow current had a negative slope and reversed sign near the resting potential. It is suggested that this current is due to a Clconductance change. 5. The stretch-induced current, consisting of a rapid transient phase and a steady component can be isolated from the slow stretch-induced current at a holding potential corresponding to the resting potential. 6. The SIC-Em relation is non-linear and reverses sign at about +15 mV. 7. In a given cell, the reversal potential of the stretch-induced potential change obtained with current clamp coincided with the 0-current potential of the stretchinduced current obtained by voltage clamp. The average value from twenty-six cells was + 13 + 6'5 mV; cell to cell variability seemed to be correlated with dendrite length. 8. Tris (mol. wt. 121) or arginine (mol. wt. 174) substituted for Na+ reduces but does not abolish the stretch-induced current. 9. The permeability ratios of Tris: Na and arginine: Na were estimated from changes in the 0-current potential as these cations replaced Na+ in the eternal medium. The PTr, :PNa was somewhat higher (0-31) than the Parginine:PN ratio (0.25). 10. Changes in the external Ca2+ concentration had no effect on the 0-current potential in Na or Tris saline. However, reducing Ca2+ did augment the stretchinduced current in either saline. A tenfold reduction of Ca2+ increased the conductance (at the 0-current level) about twofold. H. M. BROWN AND OTHERS 11. Intracellular K+ and Clactivities were obtained with ion sensitive electrodes. The average values from six cells were ai = 133 + 34 mM and ai i = 15-2 + 1-8 mM S.D.). EK was about 20 mV more negative than Em and EC1 was about 10 mV more positive than Em. 12. act and resting Em undergo large changes in K+-free solutions. After 60 min, ak was reduced eightfold and Em was reduced from-67 to-40 mV. Reduced Ca2+ in K+-free augments the rate of these changes. Receptor potential amplitude was also reduced in K+-free solution but could be restored upon polarizing the membrane to the pre-existing resting level.
SUMMARY AND CONCLUSIONS 1. Tetanic stimulation of lamprey sensory dorsal cells resulted in a posttetanic hyperpolarization (PTH). The amplitude and duration of the PTH were dependent on the stimulus duration and frequency. The PTH was not reversed at membrane potentials negative to-100 mV, whereas the afterhyperpolarization following single action potentials reversed at approximately-85 mV. There was also a biphasic effect on the input resistance during the PTH, with an early reduction that recovered to control before the PTH had decayed. 2. The amplitude and duration of the PTH were increased in Ringer solution containing tetraethylammonium and 4-aminopyri-dine, both of which broadened single action potentials, but were reduced after intracellular injection of Cs +. Ca2+-free Ringer solution , Cd2+, and Co2+ also reduced the PTH, suggesting the involvement of a Ca2+-dependent K+ conductance. However, the PTH was not reduced in Ba2+ Ringer solution, or by the Ca2+-dependent K+ channel antagonists apamin and charybdotoxin. 3. The cardiac glycoside ouabain reduced the amplitude and duration of the PTH, as did substitution of Na+ with choline or Li +. K+-free Ringer solution also reduced the PTH, whereas high-K+ Ringer solution had more variable effects. The amplitude and duration of the PTH were also dependent on temperature. These results support the involvement of an ouabain-sensitive Na-K pump in the PTH. 4. The PTH was reduced by the tachykinins substance P and physalaemin, and by Shydroxytryptamine, which blocks apamin-sensitive Ca2+-dependent K+ channels in the lamprey. However, y-aminobutyric acid, which has been reported to reduce a Ca2+-dependent K+ conductance in the dorsal cells, did not reduce the PTH. 5. These results suggest that a Ca2+-dependent K+ conductance and an Na-K electrogenic pump underlie the PTH. The PTH reduces the excitability of the dorsal cells, suggesting that it may act as a mechanism to gate sensory information entering the spinal cord.
The Journal of General Physiology
Membrane potential changes that typically evoke transmitter release were studied by recording intracellularly from the excitor axon near presynaptic terminals of the crayfish opener neuromuscular junction. Depolarization of the presynaptic terminal with intracellular current pulses activated a conductance that caused a decrease in depolarization during the constant current pulse. This conductance was identified as a calcium-activated potassium conductance, g~c~), by its disappearance in a zero-calcium/EGTA medium and its block by cadmium, barium, tetraethylammonium ions, and charybdotoxin. In addition to gK~c,), a delayed rectifier potassium conductance (gK) is present in or near the presynaptic terminal. Both these potassium conductances are involved in the repolarization of the membrane during a presynaptic action potential.
Presynaptic calcium currents at voltage-clamped excitor and inhibitor nerve terminals of crayfish
The Journal of physiology, 1996
1. A two-electrode voltage clamp was used to record calcium currents from the excitatory and inhibitory nerve terminals that innervate the crayfish (Procambarus spp.) opener muscle. Other voltage-dependent currents were blocked with tetrodotoxin, 3,4-diaminopyridine, 4-aminopyridine and tetraethylammonium. 2. The presynaptic calcium current at both excitatory and inhibitory synapses was blocked by cadmium and omega-agatoxin IVA but was not affected by omega-conotoxin GVIA, omega-conotoxin MVIIC or nifedipine, suggesting that the calcium currents flow through P-type calcium channels. 3. Current-voltage (I-V) relations at both excitatory and inhibitory synapses are similar, with current activation near -40 mV, peak current near -10 mV and current reversal at membrane potentials greater than +25 mV. I-V relations were scaled along the current axis by partial calcium current blockade with cobalt, suggesting that series resistance and space-clamp errors were small. 4. A subset of termina...
Voltage-dependent sodium and potassium, but no calcium conductances in DDT1 MF-2 smooth muscle cells
Pfl�gers Archiv European Journal of Physiology, 1991
Voltage-dependent inward and outward membrane currents were investigated in the DDT1 MF-2 smooth muscle cell line using the whole-cell patch-clamp technique. Application of a pulse protocol with subsequent depolarizing voltage steps elicited an inactivating inward current and a non-inactivating outward current. The outward current was activated at membrane potentials more positive than -35 mY, with "Cac t = 30 -40 ms. The outward current was blocked by tetraethylammonium (NEt4C1) and 3,4-aminopyridine in a dose-dependent manner (ECs0 of 5 mM and 0.5 raM, respectively). The amplitude of the outward current was linked to the potassium equilibrium potential (Vek), and tail currents reversed near V~k. The outward current was completely abolished when intracellular potassium was substituted by 106 mM caesium and 20 mM NEt4C1. The inward current was activated at potentials more positive than -30 mV with tact of 1.6-2.5 ms, and with Z~nact of 1.7--3.0 ms. Steady-state inactivation was 50% at a holding potential of -40 inV. The inward current was blocked by tetrodotoxin (ECso of0.15 gM) and dependent on the reversal potential for sodium. Voltage-dependent calcium currents could not be detected. Further, the cytoplasmic free calcium concentration, as measured using Indo-1 fluorescence, was not changed during high-potassium(40 mM)-induced depolarization. In contrast, contraction of freshly obtained hamster vas deferens tissue elicited by high-potassium(40 mM)-induced depolarization was largely inhibited by diltiazem (20 IxM). These findings showed that voltage-dependent calcium channels are not functional in DDT~ MF-2 smooth muscle cells in contrast to freshly obtained Syrian hamster vas deferens smooth muscle. It is concluded that at least two populations of voltage-dependent channels are present in DDT1 MF-2 smooth muscle cells, conducting a slow outward rectifying current carried by potassium, and a fast, inactivating sodium current.
Pfl�gers Archiv European Journal of Physiology, 1999
Calcium-activated potassium currents were studied in dissociated smooth muscle cells from human saphenous vein (HSV) using the patch-clamp technique in the whole-cell configuration. The average measured resting membrane potential (V m) was-41±2 mV (n=39), when the cells were dialysed with an intracellular pipette solution (IPS) containing 0.1 mM ethyleneglycolbis(β-aminoethylether)-N,N,N′,N′-tetraacetic acid (EGTA) (IPS-0.1 mM EGTA). When the EGTA concentration was increased to 10 mM (IPS-10 mM EGTA) V m became significantly less negative:-13±2 mV (n=23, P<0.05). These results suggest that 10 mM EGTA reduces a calcium-dependent current involved in the maintenance of V m. Depolarizing voltage steps up to +60 mV from holding potentials of-60 mV resulted in large (1-10 nA) timeand voltage-dependent outward currents. The amplitudes of total whole-cell current densities measured at voltages above-20 mV were significantly greater in the cells dialysed with IPS-0.1 mM EGTA than in those dialysed with IPS-10 mM EGTA. In the cells dialysed with IPS-0.1 mM EGTA, 0.1 mM tetraethylammonium chloride (TEA) and 50 nM iberiotoxin (IBTX), which selectively block large conductance Ca 2+-activated potassium channels (BK Ca), diminished the total current recorded at +60 mV by 45±14% (P<0.05, n=5) and 50±6% (n=8, P<0.05), respectively. These blockers at the same concentrations did not affect the total current in cells dialysed with IPS-10 mM EGTA. When tested on intact HSV rings, both 0.1 mM TEA and 50 nM IBTX elicited vessel contraction. We conclude that BK Ca channels present in HSV smooth muscle cells contribute to the maintenance of the V m and sustain a significant portion of the total voltage-activated, outward current. Finally, BK Ca channels appear to play a significant role in the regulation of HSV smooth muscle contractile activity.