Premium
Activation of the guanylate cyclase‐guanosine 3′5′ monophosphate system of colonic mucosa by N‐methyl‐N′‐nitro‐n‐nitrosoguanidine
Author(s) -
de Rubertis Frederick R.,
Craven Patricia A.
Publication year - 1977
Publication title -
cancer
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 3.052
H-Index - 304
eISSN - 1097-0142
pISSN - 0008-543X
DOI - 10.1002/1097-0142(197711)40:5+<2600::aid-cncr2820400932>3.0.co;2-n
Subject(s) - extracellular , methylnitronitrosoguanidine , gucy1b3 , stimulation , chemistry , biochemistry , guanosine , gucy1a3 , carcinogen , cyclic guanosine monophosphate , enzyme , guanylate cyclase 2c , microbiology and biotechnology , endocrinology , nitric oxide , biology , cyclase , mutant , gene
The effects of N‐methyl‐N‐nitro‐N‐nitrosoguanidine (MNNG) on the guanylate cyclase (GC)‐guanosine 3′5′ monophosphate (cGMP) system of rat colonic mucosa were studied. MNNG (1 mM) increased colonic mucosal cGMP from 1.8 ± 0.2 to 22.5 ± 2.7 pmol/mg protein in 5 minutes. Increases in response to MNNG occurred in the presence or absence of extracellular Ca 2+ , whereas the two‐fold increase in mucosal cGMP mediated by carbamylcholine was abolished by exclusion of Ca 2+ . Although GC activity of mucosal homogenates was found predominantly (90%) in the 100,000 g particulate fraction, the effects of MNNG on mucosal cGMP correlated with stimulation of 100,000 g soluble GC by this agonist. MNNG increased soluble GC 13‐fold over the corresponding basal with 4 mM Mn 2+ , and 48‐fold with 4 mM Mg 2+ as the sole available divalent cation. Compared with unstimulated GC, the MNNG‐activated soluble enzyme was less dependent upon Mn 2+ availability and effectively utilized Mg 2+ as metal co‐factor. N‐ethylmaleimide, a sulfhydryl group alkylator, inhibited MNNG stimulation of GC and cGMP. Thus, expression of these MNNG actions may involve drug interaction with tissue thiol groups. Prior incubation of MNNG with thiol antioxidants or ascorbate also suppressed MNNG stimulation of GC, possibly through direct drug reactions involving nucleophilic and electrophilic reactants. The ability of MNNG to stimulate the colonic mucosal GC‐cGMP system could be linked to its carcinogenic action.