scholarly journals The role of cyclic nucleotides in modulation of the membrane potential of the Schwann cell of squid giant nerve fibre.

1985 ◽  
Vol 363 (1) ◽  
pp. 151-167 ◽  
Author(s):  
P D Evans ◽  
V Reale ◽  
J Villegas
Keyword(s):  
Membrane Potential ◽  
Schwann Cell ◽  
Nerve Fibre ◽  
Cyclic Nucleotides

Substance P modulation of the membrane potential of the Schwann cell of the squid giant nerve fibre

Glia ◽  
1990 ◽  
Vol 3 (5) ◽  
pp. 393-404 ◽  
Author(s):  
Peter D. Evans ◽  
Vincenzina Reale ◽  
Rosa Maria Merzon ◽  
Jorge Villegas
Keyword(s):  
Membrane Potential ◽  
Substance P ◽  
Schwann Cell ◽  
Nerve Fibre

scholarly journals Octopaminergic modulation of the membrane potential of the Schwann cell of the squid giant nerve fibre

1986 ◽  
Vol 121 (1) ◽  
pp. 421-443 ◽  
Author(s):  
V. Reale ◽  
P. D. Evans ◽  
J. Villegas
Keyword(s):  
Schwann Cell ◽  
Schwann Cells ◽  
Nerve Fibre ◽  
High Frequency ◽  
Cell Activity ◽  
Physiological Role ◽  
Giant Axon ◽  
Octopamine Receptors ◽  
Low Concentrations

The actions of octopamine on the Schwann cells of the giant nerve fibre of the tropical squid are described. The pharmacology of the receptors mediating the actions of octopamine has been investigated in terms of stereospecificity, amine specificity and interactions with a range of agonists and antagonists. The receptors are maximally activated by D(−)-octopamine and share many of the characteristics of OCTOPAMINE2 class receptors in other preparations. The octopamine receptors appear to mediate their actions by increasing the intracellular levels of cyclic AMP in the Schwann cells. Low concentrations of octopamine potentiate the actions of the nicotinic cholinergic activation system of the Schwann cells. The results are discussed in terms of the possible physiological role of octopamine in the modulation of Schwann cell activity during stressful conditions when the giant axon system is likely to be used at a high frequency to facilitate the escape response of the squid.

scholarly journals N-methyl-D-aspartate (NMDA) and non-NMDA (metabotropic) type glutamate receptors modulate the membrane potential of the Schwann cell of the squid giant nerve fibre.

1992 ◽  
Vol 173 (1) ◽  
pp. 229-249 ◽  
Author(s):  
P D Evans ◽  
V Reale ◽  
R M Merzon ◽  
J Villegas
Keyword(s):  
Amino Acids ◽  
Membrane Potential ◽  
Schwann Cell ◽  
Glutamate Receptors ◽  
Nerve Fibre ◽  
Excitatory Amino Acids ◽  
Metabotropic Glutamate Receptors ◽  
Metabotropic Glutamate ◽  
Type Receptor ◽  
Lasting Change

L-Glutamate application can produce three different responses in the membrane potential of the Schwann cell of the tropical squid, Sepioteuthis sepioidea, which appear to be mediated by three pharmacologically distinct classes of receptor. A class of non-NMDA-type receptors, with some similarities to metabotropic glutamate receptors, mediates the development of a rapid and long-lasting hyperpolarization. Two pharmacologically distinct classes of NMDA-type receptor are present. One mediates the development of a slow depolarization accompanied by a long-lasting change in responsiveness of the Schwann cell. The second produces rapid depolarizing responses during the period of this changed responsiveness. All three types of receptor can be activated by dipeptides containing excitatory amino acids.

scholarly journals Endothelium-Dependent Dilation of Feline Cerebral Arteries: Role of Membrane Potential and Cyclic Nucleotides

1989 ◽  
Vol 9 (3) ◽  
pp. 256-263 ◽  
Author(s):  
Joseph E. Brayden ◽  
George C. Wellman
Keyword(s):  
Membrane Potential ◽  
Cyclic Nucleotides ◽  
Cerebral Arteries ◽  
Cyclic Adenosine Monophosphate ◽  
Adenosine Monophosphate ◽  
Cyclic Guanosine Monophosphate ◽  
Guanosine Monophosphate ◽  
Membrane Potential Change ◽  
Middle Cerebral Arteries

The objective of this study was to characterize the role of membrane potential and cyclic nucleotides in endothelium-dependent dilation of cerebral arteries. Middle cerebral arteries isolated from cats were depolarized and constricted in response to serotonin or when subjected to transmural pressures >50 mm Hg. Acetylcholine (ACh) and ADP caused vasodilation and a sustained, dose-dependent hyperpolarization of up to 20 mV in this artery. The membrane potential change preceded the vasodilation by ∼6 s. Hyperpolarizations and dilations to ACh and ADP did not occur in preparations without endothelium. The hyperpolarizations were abolished by ouabain (10−5 M), which also blocked the dilator response to ACh. However, dilations to ADP were unaffected by ouabain. Methylene blue (5 × 10−5 M), a guanylate cyclase inhibitor, had no effect on the responses to ACh or ADP in the presence or absence of ouabain. Cyclic guanosine monophosphate (cGMP) levels were not altered in cerebral arteries exposed to ACh or ADP. However, ADP did increase cyclic adenosine monophosphate levels in these blood vessels. We conclude that although membrane hyperpolarizations may be adequate to cause vasodilation, at least one other pathway of endothelium-dependent vasodilation also is present in feline cerebral arteries. Cyclic GMP does not appear to be involved in this alternate pathway of dilation.

scholarly journals The action of vasoactive intestinal peptide antagonists on peptidergic modulation of the squid Schwann cell

1988 ◽  
Vol 138 (1) ◽  
pp. 259-269 ◽  
Author(s):  
P. D. Evans ◽  
J. Villegas
Keyword(s):  
Membrane Potential ◽  
Substance P ◽  
Schwann Cell ◽  
Vasoactive Intestinal Peptide ◽  
Nerve Fibre ◽  
Giant Axon ◽  
Potency Ratio ◽  
Vip Receptors ◽  
Exogenous Application

1. The effects of two specific antagonists of vasoactive intestinal peptide (VIP) receptors were investigated on the VIP-induced hyperpolarization of the membrane potential of the Schwann cell of the giant nerve fibre of the tropical squid. 2. Both (pCl-D-Phe6,Leu17)VIP and (N-Ac-Tyr1,D-Phe2)-GRF(1–29)amide competitively and reversibly blocked the effects of VIP in this preparation with the former compound being more potent than the latter. 3. The blocking actions of both antagonists were specific for the responses of this preparation to VIP. They did not block the actions of carbachol, DL-octopamine or substance P. 4. Both antagonists also reduced the effectiveness of an endogenous VIP-like component in the normal hyperpolarizing action of giant axon activity on the membrane potential of the Schwann cell, with the same potency ratio as for their actions on the effects induced by the exogenous application of VIP.

Axon/Schwann-cell relationships in the giant nerve fibre of the squid

1981 ◽  
Vol 95 (1) ◽  
pp. 135-151
Author(s):  
J. Villegas
Keyword(s):  
Membrane Potential ◽  
Schwann Cell ◽  
Nerve Fibre ◽  
Acetylcholine Receptors ◽  
Acetylcholinesterase Activity ◽  
Feedback Mechanism ◽  
External Application ◽  
Cell Responses ◽  
Acetylcholinesterase Enzyme ◽  
Acetylcholine Concentration

This communication summarizes the experimental evidence obtained in the giant nerve fibre of the tropical squid Sepioteuthis sepioidea, on the nature of the mechanism responsible for the long-lasting effects of axonal excitation on the membrane potential of the Schwann cell. In these nerve fibres the propagation of a train of nerve impulses by the axon is followed by a prolonged hyperpolarization of the Schwann cell which can be reproduced, or modified, by the external application of cholinergic compounds. The presence and exact localization of the different components of the acetylcholine system directly involved in such Schwann-cell responses was detected by means of pharmacological, histochemical and chemical procedures. Thus, the results of the experiments herein discussed revealed that, under physiological conditions: the Schwann cell is able to synthesize, store and release acetylcholine; and that it has acetylcholine receptors of the nicotinic type, and acetylcholinesterase enzyme activity in its plasma membrane. On the other hand, the axon has low acetyltransferase activity and acetylcholine concentration in its axoplasm, and a high acetylcholinesterase activity in its axolemma. It was also found that acetylcholine hyperpolarizes the Schwann cell by increasing its relative permeability to the potassium ion. The distribution pattern of the acetylcholine system indicates that it operates as a feedback mechanism for the regulation of the Schwann-cell membrane potential and ionic permeability following axonal excitation.

scholarly journals The effect of a glutamate uptake inhibitor on axon-Schwann cell signalling in the squid giant nerve fibre.

1992 ◽  
Vol 173 (1) ◽  
pp. 251-260
Author(s):  
P D Evans ◽  
V Reale ◽  
R M Merzon ◽  
J Villegas
Keyword(s):  
Membrane Potential ◽  
Schwann Cell ◽  
Glutamate Receptors ◽  
Schwann Cells ◽  
Nerve Fibre ◽  
Glutamate Uptake ◽  
Cell Signalling ◽  
Giant Axon ◽  
Uptake System ◽  
Extracellular Level

The glutamate uptake blocker p-chloromercuriphenylsulphonic acid (PCMS) (100 mumol l-1) does not block any of the membrane potential changes induced by the application of L-glutamate to the adaxonal Schwann cells of the giant axon of the tropical squid Sepioteuthis sepioidea. This indicates that these potential changes are not due to the activation of an electrogenic glutamate uptake system and supports the idea that they are due to the activation of specific glutamate receptors. The presence of PCMS (100 mumol l-1) reduces the activity of the glutamate uptake system sufficiently for the extracellular level of axonally released glutamate to exceed the threshold for the activation of the NMDA-type glutamate receptors in this preparation.

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