Browsing by Author "SALAS, C"

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    INVOLVEMENT OF ET(A) RECEPTORS IN THE FACILITATION BY ENDOTHELIN-1 OF NONADRENERGIC NONCHOLINERGIC TRANSMISSION IN THE RAT URINARY-BLADDER
    (1994) DONOSO, MV; SALAS, C; SEPULVEDA, G; LEWIN, J; FOURNIER, A; HUIDOBROTORO, JP
    1 Endothelin-l (ET-1; 3-10nM) raised the tone of rat bladders bathed in buffer containing atropine (1 mu M) plus guanethidine (3.4 mu M). In addition, ET-1 potentiated, in a concentration-dependent fashion (1-10nM), the contractions evoked by both transmural nerve stimulation and applications of exogenous adenosine 5'-triphosphate (ATP). 2 The threshold concentration of ET-1 required to facilitate non-adrenergic non-cholinergic (NANC) transmission and potentiate ATP-induced contractions, was about 10 fold lower than that required to increase the bladder tone (3nM). 3 The ET-l-induced increase in basal tension reached its maximal effect within 60-90s. In contrast, the 7.8 mu M ATP-induced contractions increased by 50% within the first minute following incubation with 10nM ET-1 but required about 5 min to develop the maximal effect. 4 The ET-l-induced potentiation of NANC or ATP responses was long-lasting and persisted in spite of extensive washing. The recovery of the bladder excitability depended on the concentration of ET-1. Following the application of 3nm ET-1, recovery required 30 min; applications of 10nM ET-1 required at least 60 min for full recovery. 5 The ET-1-induced potentiation of responses was selective for ATP and related structural analogues. ET-1 did not modify the contractions induced by acetylcholine, 5-hydroxytryptamine, prostaglandin F-2 alpha or bradykinin. 6 The potency of ET-2 was similar to that of ET-1. ET-3 and ET-C-terminal hexapeptide were inactive up to 100M. Sarafotoxin S6b was 2 to 3 fold less potent than ET-1 whereas sarafotoxin S6c (100nM) was inactive. AGETB-9 and AGETB-89, two ET(B) receptor agonists, were also inactive (up to 100nM). 7 Removal of one or both disulphide bonds in ET-1 and tryptophan-21 formylation of ET-1, resulted in inactive peptides (up to 100nM). 8 The ET-1 receptor antagonists, BE-18257B and FR139317, blocked both the ET-1-induced rise in tone and the potentiation of ATP responses in a concentration-dependent fashion. FR139317 was at least 30 fold more potent than BE-18257B. Both antagonists blocked at lower concentrations the ET-1 increase in bladder tone as compared to the ATP potentiation. The antagonism was slowly reversible. 9 Results are consistent with the presence of ET(A) receptors in the rat bladder, which mediate both actions of ET-1. The interaction of ET-1 with purinergic mechanisms is discussed.
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    PROPERTIES OF LACCASE ISOENZYMES PRODUCED BY THE BASIDIOMYCETE CERIPORIOPSIS-SUBVERMISPORA
    (1995) SALAS, C; LOBOS, S; LARRAIN, J; SALAS, L; CULLEN, D; VICUNA, R
    Laccase is one of the ligninolytic enzymes found in liquid cultures of the fungus Ceriporiopsis subvermispora in defined medium. As an approach to a clarification of the role of laccases during the attack on lignin by the fungus, the enzyme has been characterized further. The levels of this phenol oxidase increase 2-fold in the presence of p-anisidine and are severely affected when addition of either Mn(II) or Cu(II) ions to the medium is omitted. Isoelectrofocusing allowed the resolution of two laccase isoenzymes, with pIs of 3.65 and 3.59. In rich medium, laccase activity is 10-fold higher than in salt medium, and it is not affected by the external addition of p-anisidine or Ran(II). Four isoenzymes were detected in these cultures, with pIs between 3.76 and 3.60. In a wheat bran medium, four isoenzymes with pIs in the range 3.63-3.46, plus a fifth isoenzyme of high pI (4.82), were also identified. The absorption spectrum of a pool containing the four isoenzymes from rich medium shows a maximum at 600 nn, typical of laccase possessing a type I copper atom. The molecular mass of the isoenzyme with pI 3.60 is 79 kDa, as determined by SDS/PAGE. Upon treatment with endoglycosidase F, the molecular mass of this isoform decreases to 63 kDa, indicating a high degree of glycosylation. Substrate specificity studies conducted with the four isoenzymes from rich medium and a combination of isoenzymes from salt medium showed marked differences among them. The amino-terminal sequences (24 residues) of three isoenzymes isolated from rich medium were determined. Two of them are identical, whereas the third one differs from these in three amino acid residues. The consensus sequence reveals clear homology with laccases from other microorganisms.