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  • 1
    Electronic Resource
    Electronic Resource
    The ion conductances of colonic crypts from dexamethasone-treated rats (1996)
    Springer
    Pflügers Archiv 431 (1996), S. 419-426 
    Details
    ISSN: 1432-2013
    Keywords: Colon ; Triamterene ; Amiloride ; Na+ channel ; Cl− channel ; K+ channel ; Carbachol
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract Whole-cell patch-clamp studies were performed in isolated colonic crypts of rats pretreated with dexamethasone (6 mg/kg subcutaneously on 3 days consecutively prior to the experiment). The cells were divided into three categories according to their position along the crypt axis: surface cells (s.c.); mid-crypt cells (m.c.) and crypt base cells (b.c.). The zero-current membrane voltage (V m) was −56 ± 2 mV in s.c (n = 34); −76 ± 2 mV in M.C. (n = 47); and −87 ± 1 mV in b.c. (n = 87). The whole-cell conductance (G m) was similar (8–12 nS) in all three types of cells. A fractional K+ conductance accounting for 29–67% ofG m was present in all cell types. A Na+conductance was demonstrable in s.c. by the hyperpolarizing effect onV m of a low-Na+ (5 mmol/1) solution. In m.c. and b.c. the hyperpolarizing effect was much smaller, albeit significant. Amiloride had a concentration-dependent hyperpolarizing effect onV m in m.c. and even more so in s.c.. It reducedG m by approximately 12%. The dissociation constant (K D) was around 0.2 μmol/l. Triamterene had a comparable but not additive effect (K D = 30 μmol/l,n = 14). Forskolin (10 μmol/l, in order to enhance cytosolic adenosine 3′, 5′-cyclic monophosphate or CAMP) depolarizedV m in all three types of cells. The strongest effect was seen in b. c..G m was enhanced significantly in b.c. by 83% (forskolin) to 121% [8-(4-chlorophenylthio)cAMP]. The depolarization ofV m and increase inG m was caused to large extent by an increase in Cl− conductance as shown by the effect of a reduction in bath Cl− concentration from 145 to 32 mmol/1. This manocuvre hyperpolarizedV m under control conditions significantly by 6–9 mV in all three types of cells, whilst it depolarizedV m in the presence of forskolin in m.c. and in b.c.. These data indicate that s.c. of dexamethasone-treated rats possess mostly a K+ conductance and an amiloride- and Tramterene-inhibitable Na+ conductance. m.c. and b.c. possess little or no Na+ conductance; theirV m is largely determined by a K+ conductance. Forskolin (via cAMP) augments the Cl− conductance of m.c. and b.c. but has only a slight effect on s.c.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02207281
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    Paper (German National Licenses)
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  • 2
    Electronic Resource
    Electronic Resource
    The ion conductances of colonic crypts from dexamethasone-treated rats (1996)
    Springer
    Pflügers Archiv 431 (1996), S. 419-426 
    Details
    ISSN: 1432-2013
    Keywords: Key words Colon ; Triamterene ; Amiloride ; Na+ channel ; Cl ; channel ; K+ channel ; Carbachol
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract Whole-cell patch-clamp studies were performed in isolated colonic crypts of rats pretreated with dexamethasone (6 mg/kg subcutaneously on 3 days consecutively prior to the experiment). The cells were divided into three categories according to their position along the crypt axis: surface cells (s.c.); mid-crypt cells (m.c.) and crypt base cells (b.c.). The zero-current membrane voltage (V m) was −56 ± 2 mV in s.c (n = 34); −76 ± 2 mV in m.c. (n = 47); and −87 ± 1 mV in b.c. (n = 87). The whole-cell conductance (G m) was similar (8–12 nS) in all three types of cells. A fractional K+ conductance accounting for 29–67% of G m was present in all cell types. A Na+ conductance was demonstrable in s.c. by the hyperpolarizing effect on V m of a low-Na+ (5 mmol/l) solution. In m.c. and b.c. the hyperpolarizing effect was much smaller, albeit significant. Amiloride had a concentration-dependent hyperpolarizing effect on V m in m.c. and even more so in s.c.. It reduced G m by approximately 12%. The dissociation constant (K D) was around 0.2 μmol/l. Triamterene had a comparable but not additive effect (K D = 30 μmol/l, n = 14). Forskolin (10 μmol/l, in order to enhance cytosolic adenosine 3′, 5′-cyclic monophosphate or cAMP) depolarized V m in all three types of cells. The strongest effect was seen in b.c.. G m was enhanced significantly in b.c. by 83% (forskolin) to 121% [8-(4-chlorophenylthio)cAMP]. The depolarization of V m and increase in G m was caused to large extent by an increase in Cl−conductance as shown by the effect of a reduction in bath Cl−concentration from 145 to 32 mmol/l. This manoeuvre hyperpolarized V m under control conditions significantly by 6–9 mV in all three types of cells, whilst it depolarized V m in the presence of forskolin in m.c. and in b.c.. These data indicate that s.c. of dexamethasone-treated rats possess mostly a K+ conductance and an amiloride- and triamterene-inhibitable Na+ conductance. m.c. and b.c. possess little or no Na+ conductance; their V m is largely determined by a K+ conductance. Forskolin (via cAMP) augments the Cl− conductance of m.c. and b.c. but has only a slight effect on s.c.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02207281
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 3
    Electronic Resource
    Electronic Resource
    Effects of the carcinogen dimethylhydrazine (DMH) on the function of rat colonic crypts (1996)
    Springer
    Pflügers Archiv 433 (1996), S. 254-259 
    Details
    ISSN: 1432-2013
    Keywords: Key words Dimethylhydrazine ; Carcinogenesis ; Cl ; secretion ; Na+ channel ; Amiloride
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract  Rats injected with dimethylhydrazine for 5 weeks (DMH, 40 mg/kg body weight) invariably develop colonic cancer after a latency of some 10–14 weeks. Preliminary studies have suggested that Na+ absorption by surface colonic crypt cells is attenuated in the preneoplastic period (8–12 weeks after the first injection of DMH). The present study of glucocorticoid-treated (dexamethasone 6 mg/kg body weight, s.c. 3 days or triamcinolone 30 mg/kg body weight, s.c. 3 days) rats was undertaken to examine the ion transport properties of rat distal colon during this period in more detail. Ussing chamber studies of the distal colon and whole-cell patch-clamp measurements in surface cells, mid-crypt cells and crypt-base cells obtained from isolated crypts were performed. In Ussing chamber studies the equivalent short-circuit current inhibitable by amiloride (10 μmol/l) DMH-treated rats was about 40% of control. In addition, the hyperpolarizing effect of amiloride (10 μmol/l) on membrane voltage (V m) was strongly attenuated in surface and mid-crypt cells of DMH-treated rats. Carbachol (CCH, 100 μmol/l), which predictably hyperpolarized surface, mid-crypt cells and crypt-base cells of control rats, had no significant effect on V m in DMH-treated rats, but increased membrane conductance (G m) significantly. This indicates that CCH probably activates both Cl–and K+ channels in all three colonic crypt compartments in the DMH-treated rats. Forskolin (5 μmol/l), which has the most pronounced effect in crypt-base cells in control rats, depolarized V m and enhanced G m in all three compartments in DMH-treated rats. These data indicate that DMH profoundly alters Na+ and Cl–transport in colonic crypts prior to the appearance of colonic adenocarcinoma and that these effects can be summarized as follows: (1) the Na+ conductance of surface cells is attenuated; (2) cells along the length of the crypt-lumen axis tend to lose their normal response to CCH and instead show simultaneous and comparable increases in K+and Cl–conductances; (3) the effect of forskolin is enhanced along the entire crypt axis. As a result colonic crypt transport is shifted to predominant Cl–secretion, findings which are characteristic of colonic carcinoma cell lines such as HT29 and T84 cells.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s004240050275
    Library Location Call Number Volume/Issue/Year Availability
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    Paper (German National Licenses)
    Fulltext
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