Dopamine‐induced depolarizing responses associated with negative slope conductance in LB‐cluster neurones of Aplysia.

Matsumoto, Mitsuhiko; Sasaki, Kazuhiko; Sato, Makoto; Shozushima, Masanori; Takashima, Koichiro

doi:10.1113/jphysiol.1988.sp017410

Cited by 29 publications

(20 citation statements)

References 33 publications

(60 reference statements)

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“…Neither Mg nor Ca ions appear to contribute to the current, at least in physiological solutions, because the reversal potential is unaffected by the complete removal of these divalents from the bathing medium. This finding is consistent with the data of Connor and Hockberger (1984a), who found, in Archidoris neurons, that the response that was eliminated in Nafree solutions was not associated with an increase in intracellular Slow inward Current i n Ap/ysia Neurons Ca as measured with arsenazo signals (see also the CAMP-induced current in Matsumoto et al, 1988). Slightly different conclusions, however, were drawn from certain previous studies on other neurons (e.g., in Helix by Kononenko et al, 1983;Swandulla and Lux, 1984; in Limax by Connor and Hockberger, 1985; in Apfysia by Hara et al, 1985).…”

Section: +25supporting

confidence: 92%

“…In all previously published studies but 1 (Kononenko et al, 1983; see below), a dramatic enhancement of the response was seen when (Ca), was lowered (Aldenhoff et al, 1983;Hara et al, 1985;Kehoe, 1985a;Gillette and Green, 1987;Matsumoto et al, 1988). This finding is, of course, contrary to that which would be expected if Ca contributed directly to the current and suggests that this divalent cation, rather than carrying the current, exerts an inhibitory effect upon it.…”

Section: +25mentioning

confidence: 78%

“…One of the characteristics of the CAMPinduced inward current is its failure to increase in amplitude with hyperpolarization of the cell membrane beyond the resting potential (see Aldenhoff et al, 1983;Connor and Hockberger, 1984a;Kehoe, 1985a;Matsumoto et al, 1988). Two experiments showing the voltage dependence of this response are illustrated in Figure 1, where the raw data are presented in A and B and the current amplitudes plotted against holding potential are shown in C. As can be seen in Figure lC, there is even a decrease in the amplitude of the response to the nucleotide injection as the membrane is hyperpolarized from -40 towards -100 mV.…”

Section: Resultsmentioning

confidence: 99%

“…Earlier investigations showed that changes in extracellular K concentration had no effect on the amplitude of the CAMP-induced response at resting potential (e.g., Connor and Hockberger, 1984a;Hara et al, 1985;Matsumoto et al, 1988;J. Kehoe, unpublished observations).…”

Section: +25mentioning

confidence: 93%

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Cyclic AMP-induced slow inward current in depolarized neurons of Aplysia californica

Kehoe

1990

J. Neurosci.

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Cyclic nucleotides have been implicated in many long-lasting transmitter-induced effects on membrane conductance. One previously observed effect of cAMP on molluscan neurons is to induce a slow inward current, which has been further evaluated here in depolarized anterior and medial cells of the pleural ganglion of Aplysia californica in order to understand better its underlying ionic mechanisms and its sensitivity to a variety of pharmacological agents. This current, which appears to be the only cAMP-induced current seen in the anterior cells, was shown to invert at about +25 mV, that is, approximately 25-30 mV inferior to ENa. This reversal potential was lowered by about 15-16 mV when half of the extracellular Na was replaced by either mannitol or N- methyl-D-glucamine, whereas it was unaffected by changes in extracellular Cl, Ca, or Mg. The response persisted in seawater in which the Na had been totally replaced by K, and its reversal potential shifted towards more negative values. These data are consistent with the hypothesis that both Na and K ions permeate the channel, with a Na/K permeability ratio of approximately 2. Ca ions do not appear to permeate the channel, but they do have a marked inhibitory effect on the response amplitude, as do Mg ions when Ca is not present. Caffeine, intracellular acidification, and phosphodiesterase inhibitors enhance and prolong the response without changing its reversal potential. Previous studies have shown that both caffeine and intracellular acidification inhibit phosphodiesterase, and it is assumed that the common effect of these manipulations on the cAMP-induced inward current is mediated, at least partially, by the inhibition of that enzyme. In the medial cells of the pleural ganglion, this slow inward current is present, but is dominated in the depolarized cell by a cAMP-induced diminution in a Ca-activated K conductance (Kehoe, 1985b). This K conductance and, consequently, the noninverting, cAMP-induced inward current that reflects its diminution, were shown to disappear in Ca- free solutions, in the presence of isobutyl-1-methylxanthine (IBMX) or caffeine, and upon acidification of the cytoplasm. When this cAMP- sensitive K conductance is blocked, the presence of the inverting cAMP- induced cationic current is unmasked. The cAMP-induced cationic current is shown to have many properties in common with cyclic nucleotide- induced currents described in photoreceptors, olfactory receptor cilia, and cardiac myocytes, all of which have been shown to be outwardly rectifying cationic currents that are inhibited by divalent cations and do not involve the activation of a cAMP-dependent kinase.

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Section: +25supporting

confidence: 92%

Section: +25mentioning

confidence: 78%

Section: Resultsmentioning

confidence: 99%

Section: +25mentioning

confidence: 93%

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Cyclic AMP-induced slow inward current in depolarized neurons of Aplysia californica

Kehoe

1990

J. Neurosci.

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“…Similar results were observed in other three cells that had the same type of ACh-receptors. (Matsumoto et al 1988).…”

Section: Effects Of Fm On the Cv-dependent Hyperpolarizing Responsesmentioning

confidence: 99%

Effects of furosemide on the resting membrane potentials and the transmitter-induced responses of the Aplysia ganglion cells.

Nakai

Sasaki

Matsumoto

et al. 1988

Tohoku J. Exp. Med.

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Calcitonin induces a decreased Na⁺ conductance in identified neurons of Aplysia

Sawada

Ichinose

Ishikawa

et al. 1993

J of Neuroscience Research

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The ionic mechanism of the effect of extracellularly ejected calcitonin (CT) on the membrane of identified neurons R9 and R10 of Aplysia was investigated with voltage-clamp, micropressure ejection, and ion substitution techniques. Micropressure-ejected CT caused a marked hyperpolarization in the unclamped neuron. Heat-inactivated CT was without effect. Clamping the same neuron at its resting potential level (-60 mV) and re-ejecting CT with the same dose produced a slow outward current (Io(CT), 30-40 sec in duration, 4-6 nA in amplitude) associated with a decrease in input membrane conductance. Io(CT) was decreased by depolarization and increased by hyperpolarization. The extrapolated reversal potential of Io(CT) was approximately +10 mV. Io(CT) was sensitive to changes in the external Na+ concentration but not to changes in K+, Ca2+, and Cl- concentrations. Micropressure-ejected forskolin produced a slow outward current, which, like the current to CT, was associated with a decrease in input membrane conductance, and was sensitive to changes in the external Na+ concentration. Io(CT) was prolonged by bath-applied isobutylmethylxanthine (IBMX) but was not affected by 1-oleoyl-2-acetylglycerol (OAG) and calphostin C. Neither superfusion of the neuron with nordihydroguaiaretic acid (NDGA) nor superfusion with indomethacin caused any changes in Io(CT). These results suggest that extracellular CT can induce a slow outward current associated with a decrease in Na+ conductance, mediated by a receptor-controlled increase in intracellular cyclic adenosine 3',5'-monophosphate.

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Dopamine‐induced depolarizing responses associated with negative slope conductance in LB‐cluster neurones of Aplysia.

Cited by 29 publications

References 33 publications

Cyclic AMP-induced slow inward current in depolarized neurons of Aplysia californica

Cyclic AMP-induced slow inward current in depolarized neurons of Aplysia californica

Effects of furosemide on the resting membrane potentials and the transmitter-induced responses of the Aplysia ganglion cells.

Calcitonin induces a decreased Na⁺ conductance in identified neurons of Aplysia

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Dopamine‐induced depolarizing responses associated with negative slope conductance in LB‐cluster neurones of Aplysia.

Cited by 29 publications

References 33 publications

Cyclic AMP-induced slow inward current in depolarized neurons of Aplysia californica

Cyclic AMP-induced slow inward current in depolarized neurons of Aplysia californica

Effects of furosemide on the resting membrane potentials and the transmitter-induced responses of the Aplysia ganglion cells.

Calcitonin induces a decreased Na+ conductance in identified neurons of Aplysia

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Calcitonin induces a decreased Na⁺ conductance in identified neurons of Aplysia