The ion conductances of colonic crypts from dexamethasone-treated rats

D. Ecke, M. Bleich, B. Schwartz, G. Fraser, R. Greger

Research output: Contribution to journalArticlepeer-review

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 (Vm) 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 (Gm) was similar (8 12 nS) in all three types of cells. A fractional K+ conductance accounting for 29-67% of Gm was present in all cell types. A Na+ conductance was demonstrable in s.c. by the hyperpolarizing effect on Vm 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 Vm in m.c. and even more so in s.c.. It reduced Gm by approximately 12%. The dissociation constant (KD) was around 0.2 μmol/l. Triamterene had a comparable but not additive effect (KD = 30 μmol/l, n = 14). Forskolin (10 μmol/l, in order to enhance cytosolic adenosine 3′, 5′-cyclic monophosphate or cAMP) depolarized Vm in all three types of cells. The strongest effect was seen in b.c.. Gm was enhanced significantly in b.c. by 83% (forskolin) to 121% [8-(4-chlorophenylthio)cAMP]. The depolarization of Vm and increase in Gm 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 Vm under control conditions significantly by 6-9 mV in all three types of cells, whilst it depolarized Vm 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 Vm 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.

Original languageEnglish
Pages (from-to)419-426
Number of pages8
JournalPflugers Archiv European Journal of Physiology
Volume431
Issue number3
DOIs
StatePublished - 1996

Keywords

  • Amiloride
  • Carbachol
  • Cl channel
  • Colon
  • K channel
  • Na channel
  • Triamterene

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