Effect of calcium upon sodium inactivation in the giant axon ofLoligo pealei

SUMMARY1. The effect of external and internal electrolytes on the parameters of the Na conductance, in particular on the time constant of removal of Na inactivation, was studied in intact and perfused squid giant axons under voltage-clamp conditions.2. Adding 20-40 mM-KCl, -CsCl or -RbCl to K-free sea water reversibly increased the time constant of removal of inactivation by a factor of about 1P3; adding 20 mM-NaCl had no effect. The time constant of development of inactivation was decreased. The results are consistent with a -5 mV shift of the Th( V) curve. The sodium activation (m3 ) and inactivation (h9) curves were shifted by the same amount.3. Raising external Ca, by contrast, decreased the time constant of removal of inactivation and increased the time constant of development of inactivation, i.e. shifted the rh( V) curve to more positive internal potentials. A free Ca concentration of 0 1 mm in the internal solution had no effect on Na inactivation.4. The observations are compatible with the idea that external K, Cs or Rb interfere with the binding of Ca to negative fixed charges at the outer side of the membrane, thereby causing a shift in the opposite direction to the shift produced by raising external Ca.5. Replacing two thirds of the internal K by Na reversibly increased the time constant of removal of sodium inactivation and moved the Th( V) curve in the vertical direction.

supporting

confidence: 88%

Section: Effect Of Internal K and Na On The Time Constant Thsupporting

confidence: 56%

Section: Effect Of External Ca On the Time Constant Thmentioning

confidence: 99%

See 1 more Smart Citation

The effect of external potassium on the removal of sodium inactivation in squid giant axons.

Gillespie¹,

Meves²

1981

“…This is not the combination produced by esters and ketones. Reduction of the external calcium concentration does result in both a hyperpolarizing shift and a flattening of the hoo curve (Frankenhaeuser & Hodgkin, 1957;Shoukimas, 1978). However, to achieve the required magnitude of shifts, treatment with esters or ketones would have to reduce the calcium concentration in the appropriate region by a factor of 5-10.…”

Section: Discussionmentioning

confidence: 99%

Anaesthetic action of esters and ketones: evidence for an interaction with the sodium channel protein in squid axons.

Elliott¹,

Haydon²,

Hendry³

1984

SUMMARY1. The effects of methyl butyl ketone, methyl heptyl ketone and methyl pentanoate on the sodium current of the squid giant axon have been examined.2. The peak inward current in intact axons was reduced reversibly by each substance. Sodium currents were recorded in intracellularly perfused axons before and during exposure to the test substances and the records were fitted with equations similar to those proposed by Hodgkin & Huxley (1952).3. Shifts in the voltage dependence of the steady-state activation and inactivation parameters (m., and h.), reductions in the peak heights of the activation and inactivation time constants (Tm and rh) and changes in the maximum sodium conductance (iNa) caused by these substances have been tabulated and compared with the effects of methyl octanoate (Haydon & Urban, 1983b). 4. Each compound shifted the voltage dependence of the steady-state inactivation parameter in the hyperpolarizing direction and that of the steady-state activation parameter in the depolarizing direction. The shifts produced by the ketones are compared with those produced by methyl pentanoate and by methyl octanoate. The possible role of an interaction between the carbonyl oxygen of the test substance and the sodium channel protein in producing the h. shift is discussed.5. The peak time constants are reduced and the voltage dependences of rm and Th are shifted in a direction commensurate with the shifts in steady-state properties.6. The maximum sodium conductance is not much affected either by the ketones or by methyl pentanoate. Large reductions in peak inward current coupled with little effect on gNa have been reported for the n-alkanols and other surface-active compounds (Haydon & Urban, 1983 b). This lack of a large effect on GNa indicates that whatever direct interaction does take place between the test substance and the channel protein, it does not result in a blockage of the channel.

“…Two hypotheses have been proposed to explain the effect of divalent cations on the voltage dependence of channel gating; one is a non-specific screening of fixed negative charges on the outer cell membrane (Frankenhaeuser & Hodgkin, 1957;McLaughlin, Szabo & Eisenman, 1971;D'Arrigo, 1973;Hahin & Campbell, 1983), the other is specific binding to a negatively charged component of the channel apparatus (Hille, 1968;Hille, Woodhull & Shapiro, 1975;Shoukimas, 1978;Gilly & Armstrong, 1982a, b). These are not mutually exclusive, and local charge screening via binding to specific phospholipids close to the channel should also be considered.…”

mentioning

confidence: 99%

A modulatory action of divalent cations on transient outward current in cultured rat sensory neurones.

Mayer

Sugiyama

1988

152

SUMMARY1. The effects of some divalent cations on the A-current (IA) in cultured rat dorsal root ganglion cells (DRGs) were studied using whole-cell patch recording.2. IA was not affected by omission of calcium from the external medium; however it was significantly depressed by manganese (10 mm) applied by pressure ejection. This depressant effect of manganese resulted from a depolarizing shift of the activation curve by 17 mV, associated with only a slight reduction of the maximum conductance. At 10 mm manganese also caused a depolarizing shift of the steadystate inactivation curve by 34 mV. Divalent cations other than manganese also gave positive shifts of the steady-state activation and inactivation curves for IA but were of different potency; the sequence was: Cd2+ > Mn2+ = Co2+ > Ca2+ > Mg2+. 4. In contrast to its effect on IA' manganese (10 mM) did not cause any appreciable change in the voltage dependence of the activation curve for the delayed rectifier K+ current. 5. A low concentration of manganese (1 mM) increased the amplitude Of IA recorded at pre-pulse potentials ranging from -50 to -70 mV. This augmentation of IA resulted from a positive shift of the inactivation curve by 6 mV without an appreciable shift of the activation curve; as a result a population of A-channels is released from inactivation over pre-pulse potentials from -50 to -70 mV.6. These results show that divalent cations can evoke a depolarizing shift of both the activation and inactivation gates controlling IA; this causes either depression or augmentation of IA, depending on the species and concentration of the divalent cation, and also on the pre-pulse potential used to de-inactivate IA. This modulatory effect of divalent cations on the gating Of IA appears to reflect binding to a specific, saturable site, either the A-channel protein itself, or phospholipids electrically close to the gating apparatus.