Browsing by Author "SILVA, M"

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    NEUROPEPTIDE-Y (NPY), AN ENDOGENOUS PRESYNAPTIC MODULATOR OF ADRENERGIC NEUROTRANSMISSION IN THE RAT VAS-DEFERENS - STRUCTURAL AND FUNCTIONAL-STUDIES
    (1988) DONOSO, V; SILVA, M; STPIERRE, S; HUIDOBROTORO, JP
    The role of neuropeptide tyrosine (NPY) on adrenergic neurotransmission was assessed in the rat vas deferens transmurally stimulated with square pulses of 0.15 or 15 Hz. Nanomoles of NPY inhibited the electrically-induced contractions on the prostatic half but not on the prostatic half but not on the epididymal end of the ductus. NPY was at least 200-fold more potent than norepinephrine or adenosine to produce an equivalent inhibition. Complete amino acid sequence of NPY is required for full agonist activity; deletion of tyrosine at the amino terminus, i.e., NPY fragment 2-36 was 3-fold less potent than the native peptide. NPY fragment 5-36, 11-36 or 25-36 were proportionally less potent than NPY. Avian pancreatic polypeptide was inactive. The presynaptic nature of the NPY acitivity was established measuring the outflow of 3H-norepinephrine from the adrenergic varicosities of the vas deferens electrically stimulated. In this assay, NPY was more potent than NPY 2-36 or NPY fragment 5-36. No inhibitory action of NPY was detected in K+ depolarized tissues. The inhibitory effect of NPY on the rat vas deferens neurotransmission was not significantly modified by yohimbine, theophylline or naloxone, indicating that the effect of NPY is not due to the activation of alpha2-adrenoceptors, adenosine receptors or opiate receptors respectively. Picrotoxin or apamin did not modify the inhibitory potency of NPY; verapamil or methoxyverapamil significantly reduced its potency. The inhibitory action of NPY is best explained through the activation of presynaptic NPY receptors that regulate norepinephrine release via a negative feedback mechanism. Structure activity studies give support to the notion of NPY receptors.
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    THE MAJOR THIOBACILLUS-FERROOXIDANS OUTER-MEMBRANE PROTEIN FORMS LOW CONDUCTANCE ION CHANNELS IN PLANAR LIPID BILAYERS
    (1992) SILVA, M; FERREIRA, A; RODRIGUEZ, M; WOLFF, D
    A protein isolated and purified from the outer membrane of the acidophilic, chemolithotrophic bacterium, Thiobacillus ferrooxidans with an oligomeric molecular weight of 90 000 Da (p90) was incorporated into phosphatidylethanolamine planar lipid bilayers. The protein formed slightly anionic channels in KCl solutions, with a conductance of 25 pS in 100 mM KCl. The current-voltage relationship was linear between +/-60 mV, and the conductance was a saturating function of the salt concentration. These channels fluctuated from a single open to closed state at low potentials, but present flickering activity at higher potentials.