Kinetics of G protein-mediated modulation of the potassium M-current in bullfrog sympathetic neurons

López, Héctor S.

doi:10.1016/0896-6273(92)90093-s

Cited by 27 publications

(20 citation statements)

References 39 publications

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“…In addition, the proportion of channels tonically inhibited calculated from the rate of spontaneous reduction in cells dialyzed with GTPrS (0.009 seer) (Lopez, 1992) and the rate of recovery (0.046 see-I) is 16%, which is insufficient to account for a 60% increase in the current during overrecovery. Therefore, there are three alternatives for the origin of overrecovery:…”

Section: Discussionmentioning

confidence: 99%

“…Figure 3A shows the response to different concentrations of agonist. With higher concentrations of agonist there was more M-current inhibition and the rate was faster (see also Lopez, 1992). Additionally, the delay ofthe response decreased as the rates ofinhibition became faster.…”

Section: Methodsmentioning

confidence: 98%

“…The rate constant of recovery was 0.046 + 0.013 see-I (n = 43) (time constant, 21.7 set), and the rate constant of recovery from overrecovery was 0.0 13 f 0.005 set-I (n = 32) (time constant, 76.9 set). The unbinding of muscarine from the receptor is unlikely to be rate limiting, because the concentration that produces 50% of maximal inhibition is on the order of 0.5-1.0 PM (Adams et al, 1982b;Lopez, 1992), and, assuming a binding rate of at least 3.10' M-'set-I, it can be calculated (Jones, 1992) that the time constant for unbinding of muscarine would be at least -70 msec (rate -15 see-I).…”

Section: Methodsmentioning

confidence: 99%

“…It has been observed in calcium currents (Boland and Bean, 1993) and in other preparations (Forscher et al, 1986;Kasai, 1991;Yakel, 1991). Previous analysis has shown that the rate of recovery of Z, from inhibition is slow (Jones, 1992;Lopez, 1992) that the rate of inhibition increases with agonist concentration in cells dialyzed with GTPyS (Lopez, 1992) and that the rate of inhibition is reduced in cells dialyzed with GDPpS (Simmons et al, 1992). Interestingly, the reduction in the rate of inhibition of I, by internal GDPpS is specific to the agonist (muscarine, LHRH, or substance P) used to evoke the response (Simmons and Mather, 1991).…”

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confidence: 99%

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On the role of arachidonic acid in M-current modulation by muscarine in bullfrog sympathetic neurons

Villarroel

1994

J. Neurosci.

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The modulation by muscarine or LHRH of the potassium M-current (IM) in whole-cell voltage-clamped bullfrog sympathetic neurons presents an initial phase of current reduction, followed, after agonist removal, by a transient enhancement or “overrecovery.” Employing a fast solution exchange system, an inhibitory process and an enhancing process were distinguished kinetically. The extent of overrecovery increased with the extent of the preceding inhibition. The rate and degree of inhibition increased with the concentration of agonist. In contrast, the rate of recovery and the extent of overrecovery were independent. The half-lives of the inhibitory and enhancing processes were 21 and 53 sec, respectively. Several observations suggest that arachidonic acid (AA) may be involved in overrecovery: (1) AA enhanced IM in a dose- dependent and reversible manner, with an IC50 of 2.8 microM. (2) Muscarine inhibited the A-current (IA), a potassium current that is blocked by AA. (3) Phospholipase A2 inhibitors (quinacrine and bromophenacyl bromide) and a lipoxygenase inhibitor (nordihydroguaiaretic acid) prevented overrecovery, without affecting the rate or extent of IM inhibition significantly. However, kinetic analysis indicates that these drugs were preventing overrecovery by prolonging the half-life of the inhibitory process to > 80 sec (e.g., not necessarily by blocking the enhancing pathway). In addition, the extent of IA inhibition was less than expected if AA was mediating both IM enhancement and IA inhibition. The observed relation between extent and rate of overrecovery, and the action of arachidonic acid metabolism inhibitors can be accounted for by a model proposing that the agonist alters the equilibrium between three pools of M-channels.

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Section: Discussionmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 98%

Section: Methodsmentioning

confidence: 99%

mentioning

confidence: 99%

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On the role of arachidonic acid in M-current modulation by muscarine in bullfrog sympathetic neurons

Villarroel

1994

J. Neurosci.

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“…Scale bar for A-C is 15 pm and is positioned at the level of the coverslip in C. Color bar indicates relative fluorescent intensity in this and subsequent images. perfusion and details of pipette geometry are described more fully in other work performed in the lab of Paul Adams (Lopez, 1992;Yu et al, 1994).…”

Section: Methodsmentioning

confidence: 99%

Calcium permeability of the neuronal nuclear envelope: evaluation using confocal volumes and intracellular perfusion

O'Malley

1994

J. Neurosci.

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In many calcium-imaging studies, the nuclear envelope appears to maintain a gradient of free calcium between the nucleus and cytosol. This issue was examined by loading amphibian sympathetic neurons with the calcium indicator fluo 3 via whole-cell patch clamping. Confocal optical sectioning allowed acquisition of independent calibration curves for the nucleus and cytoplasm. Cells were loaded with free calcium levels ranging from 10 nM to 50 microM, using 10 mM BAPTA to control free calcium. The nuclear fluorescence was usually about 130% brighter than the cytoplasmic fluorescence. Had the increased nuclear fluorescence been due to a calcium gradient, then, as fluo 3 was saturated with calcium in both compartments, the fluorescence gradient should have gradually disappeared. Instead, with free-calcium in the pipette set at 50 microM, about five times the level required to nearly saturate fluo 3, the nuclear/cytoplasmic (N/C) fluorescence ratio was not decreased but instead increased slightly. Perfusion of the patch pipette was used in conjunction with imaging to confirm that cytoplasmic fluo 3 was saturated with calcium. After loading cells with 10 nM free calcium, the patch pipette was perfused with high calcium (10 microM). Again, the N/C fluorescence ratio increased at high calcium. The effectiveness of patch-pipette perfusion in changing cellular free calcium levels was indicated by the degree of fluorescence increase--both nuclear and cytosolic compartments showed a roughly 20-fold increase in fluorescence, that is, most of the dynamic range observed in test droplets. To confirm further that cytoplasmic fluo 3 was saturated, cells were perfused with manganese, which binds with very high affinity to fluo 3. Manganese rapidly entered the cytoplasm and nucleus, causing a large increase in fluorescence, but the N/C fluorescence ratio remained relatively constant. Because free manganese in the pipette was 50,000 times the amount required to saturate fluo 3, the greater nuclear fluorescence probably results from additional fluo 3 in the nucleus rather than from calcium or manganese gradients. To gauge further the permeability of the nuclear envelope, the diffusion of calcium was visualized. Under voltage clamp, calcium channels were opened for periods ranging from 5 to 200 msec. Peak calcium levels were observed within 2 microns of the plasma membrane, and declined as calcium diffused into the cell. The nuclear fluorescence increased more than cytosolic fluorescence, but this apparent “amplification” was eliminated by correcting for autofluorescence. Use of cells cultured on glass coverslips and a high- NA microscope objective allowed a satisfactory correction.(ABSTRACT TRUNCATED AT 400 WORDS)

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The effect of arachidonic acid on the M current of NG108-15 neuroblastoma � glioma hybrid cells

1992

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The M current, IM, a voltage-dependent non-inactivating K+ current, was recorded in NG108-15 neuroblastoma x glioma hybrid cells, using the whole-cell mode of the patch-clamp technique. We studied the effect of arachidonic acid, other fatty acids and inhibitors of the arachidonic acid metabolism. In relatively high concentrations (25-50 microM) arachidonic acid first increased and later decreased the current, Ih, which holds the membrane potential at -30 mV and mainly flows through open M channels. It shifted the midpoint potential, Vo, of the relation between M conductance, gM, and membrane potential, V, to more negative values and decreased the maximum conductance gM and the time constant tau M. In smaller concentrations (5-10 microM) arachidonic acid merely decreased Ih and gM with little effect on Vo and tau M. Eicosatetraynoic acid and docosahexaenoic acid acted similarly to arachidonic acid whereas stearic acid had no effect. Of the three enzyme inhibitors studied, nordihydroguaiaretic acid acted similarly to arachidonic acid. i.e. caused a biphasic change in Ih. Indomethacin and quinacrine caused, respectively, a pure increase and a pure decrease of Ih and gM. Possible explanations are build-up of internally produced arachidonic acid, depletion of eicosanoid products or an inhibitory effect unrelated to arachidonic acid metabolism.

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Kinetics of G protein-mediated modulation of the potassium M-current in bullfrog sympathetic neurons

Cited by 27 publications

References 39 publications

On the role of arachidonic acid in M-current modulation by muscarine in bullfrog sympathetic neurons

On the role of arachidonic acid in M-current modulation by muscarine in bullfrog sympathetic neurons

Calcium permeability of the neuronal nuclear envelope: evaluation using confocal volumes and intracellular perfusion

The effect of arachidonic acid on the M current of NG108-15 neuroblastoma � glioma hybrid cells

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