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Evidence for metabotropic function of epithelial nicotinic cholinergic receptors in rat colon
Author(s) -
Lottig Lena,
Bader Sandra,
Jimenez Marcel,
Diener Martin
Publication year - 2019
Publication title -
british journal of pharmacology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.432
H-Index - 211
eISSN - 1476-5381
pISSN - 0007-1188
DOI - 10.1111/bph.14638
Subject(s) - chemistry , biophysics , nicotinic agonist , ionotropic effect , cytosol , ionomycin , metabotropic receptor , muscarinic acetylcholine receptor , bapta , microbiology and biotechnology , receptor , biochemistry , intracellular , biology , glutamate receptor , enzyme
Background and Purpose ACh exerts its actions via nicotinic (nAChR) and muscarinic receptors. In the peripheral nervous system, ionotropic nAChR mediate responses in excitable cells. However, recent studies demonstrate the expression of nAChR in the colonic epithelium, which are coupled to an induction of Cl − secretion via activation of the Na + ‐K + ‐pump. Experimental Approach In order to find out whether these epithelial nAChR function as ionotropic receptors, intracellular microelectrode and imaging experiments were performed in isolated crypts from rat colon. Apically permeabilized epithelia were used to measure pump current across the basolateral membrane. Key Results Imaging experiments with the Na + ‐sensitive dye SBFI revealed that nicotine induced a decrease in the cytosolic Na + concentration concomitant with a fall in the cytosolic Ca 2+ concentration in about 50% of the cells. as shown in fura‐2 experiments. Nicotine hyperpolarized the membrane by 6.4 ± 2.1 mV. These observations contradict the assumption that epithelial nAChR function as ligand‐gated non‐selective cation channels. The decrease in the cytosolic Na + concentration was strongly delayed, when the Na + ‐K + ‐pump was inhibited by scilliroside. Ussing chamber experiments revealed a strong dependence of the nicotine‐induced pump current on the presence of Ca 2+ , and chelation of cytosolic Ca 2+ with BAPTA prevented the fall in the cytosolic Na + concentration in SBFI‐loaded crypts. Inhibition of PKC with GF 109203X or Goe 6983 significantly reduced the nicotine‐induced pump current. Conclusions and Implications These results suggest that epithelial nAChR activate the Na + ‐K + ‐pump via a PKC dependent on a sufficient cytosolic Ca 2+ concentration.