Electrophysiological activity of the C-peptide of the Locusta insulin-related peptide. Effect on the membrane conductance of Locusta neurones in vitro.
The C-peptide of Locusta insulin-related peptide, which is a 50 residue peptide originally isolated from the corpora cardiaca of the insect Locusta migratoria and to which we refer as 5-kDa peptide, has been synthesised chemically by the solid-phase method, using a BOC strategy. Since this peptide contains in its sequence a potential monobasic cleavage site, we also synthesised its 1-38 residue-related fragment, named 4-kDa peptide, although we have no hints of its natural occurrence in the corpora cardiaca. Electrophysiological studies have shown that both the 5-kDa and 4-kDa peptides depolarise the membrane and increase the membrane conductance of neurones freshly isolated from the thoracic ganglia of Locusta. Under voltage-clamp conditions, the current underlying these effects was inwardly directed and could be resolved into 2 components. One component, I(5-kDa)1, activated at potentials more hyperpolarised than -50 mV, peaked at about -75 mV and was blocked by the potassium channel blockers cesium and rubidium. The second component, I(5-kDa)2 was activated at potentials more depolarised than -50 mV, increased with depolarisation and was not blocked by cesium and rubidium. The effects of the 5-kDa and 4-kDa peptides on the membrane potential and membrane conductance of Locusta neurones suggest that these peptides may have a physiological role in the central nervous system of insects.
Bermudez
I
I
School of Biological and Molecular Sciences, Oxford Polytechnic, Headington, England.
Beadle
D J
DJ
Trifilieff
E
E
Luu
B
B
Hietter
H
H
D000818:Animals; D002096:C-Peptide / Q000737:chemistry / Q000502:physiology*; D006110:Grasshoppers / Q000737:chemistry*; D008564:Membrane Potentials / Q000187:drug effects*; D008970:Molecular Weight; D009474:Neurons / Q000187:drug effects / Q000502:physiology; D009479:Neuropeptides / Q000737:chemistry / Q000502:physiology*; D013909:Thorax / Q000294:innervation
D002096:C-Peptide; D009479:Neuropeptides