Effects of protein reagents on electrotonic coupling in crayfish septate axon.

A. Campos de Carvalho, F. Ramon, David C. Spray

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Abstract

The lateral giant axons of the crayfish nerve cord are composed of segments contributed by each ganglion, which are electrotonically coupled by way of gap junctions. We have investigated the involvement of protein residues in regulating the resistance of crayfish junctional channels by determining effects of group-specific protein reagents. When applied to well-coupled axons, the sulfhydryl group reagents N-ethylmaleimide (NEM) and diamide uncoupled the segments; junctional resistance (Rj) was increased without changing membrane resistance or axoplasmic pH (pHi). The uncoupling produced by NEM could be reversed by alkalinization of the cytoplasm (addition of ammonium chloride to the external medium). Another sulfhydryl reagent (p-chloromercuribenzoic acid) increased Rj to a lesser extent. A disulfide reagent and three amino and three carboxyl group reagents had no effect on the Rj of these axons. The effect of group-specific reagents on partially uncoupled axons was tested by applying the drugs to axons previously exposed to weak acids. N-ethoxycarbonyl-2-ethoxy-1,2-dihydroquinoline recoupled partially uncoupled axons by decreasing Rj and prevented subsequent uncoupling of the junction by low pHi. Another carboxyl group reagent, as well as sulfhydryl and amino group reagents, either had no effect or uncoupled the axons further by increasing Rj. These experimental results suggest that amino acid residues, possibly containing carboxyl and sulfhydryl groups, control the opening and closing of junctional channels and may thus be associated with the channels' active sites.

Original languageEnglish (US)
JournalThe American journal of physiology
Volume251
Issue number1 Pt 1
StatePublished - Jul 1986
Externally publishedYes

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Astacoidea
Axons
Proteins
Sulfhydryl Reagents
Ethylmaleimide
p-Chloromercuribenzoic Acid
Diamide
Ammonium Chloride
Gap Junctions
Ganglia
Disulfides
Catalytic Domain
Cytoplasm
Amino Acids
Control Groups
Acids
Membranes
Pharmaceutical Preparations

ASJC Scopus subject areas

  • Medicine(all)

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Effects of protein reagents on electrotonic coupling in crayfish septate axon. / Campos de Carvalho, A.; Ramon, F.; Spray, David C.

In: The American journal of physiology, Vol. 251, No. 1 Pt 1, 07.1986.

Research output: Contribution to journalArticle

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