Cholinergic responses in cloned human TE671/RD tumour cells.
The cholinergic responses of the human tumour cell line TE671/RD were examined using digital Ca2+ imaging fluorescence microscopy and patch-clamp measurements. In response to stimulation of the muscarinic acetylcholine (ACh) receptor (mAChR), the intracellular concentration of Ca2+ ([Ca2+]i) rose about two-fold, in parallel with inositol 1,4,5-trisphosphate accumulation, measured by chromatographic techniques. By contrast, there was no increment of [Ca2+]i upon stimulation of the nicotinic ACh receptor (nAChR), nor after caffeine application. Electrophysiological experiments showed that TE671/RD cells lack functional voltage-activated Ca2+ channels. The stimulation of the nAChR induced transient whole-cell currents (IACh). Little or no current was detected in isotonic extracellular Ca2+, with Cs+ in the patch pipette. Cell pretreatment with muscarine reduced IACh by about 20%, without consistent modifications of current kinetics. Muscarine applied to the extra-patch membrane under the cell-attached configuration had no obvious effect on ACh-evoked unitary events. In conclusion, in human TE671/RD cells, muscarinic stimulation increases [Ca2+]i, while nicotinic stimulation does not. In addition, the nAChR exhibits peculiar ion permeability properties and is not functionally regulated by the breakdown of phosphoinositides.
Grassi
F
F
Dipartimento di Medicina Sperimentale, Università di Roma La Sapienza, Italy.
Giovannelli
A
A
Fucile
S
S
Mattei
E
E
Eusebi
F
F
D000109:Acetylcholine / Q000494:pharmacology; D001285:Atropine / Q000494:pharmacology; D002110:Caffeine / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism*; D015220:Calcium Channels / Q000502:physiology; D003001:Cloning, Molecular; D004553:Electric Conductivity; D006801:Humans; D007091:Image Processing, Computer-Assisted; D015544:Inositol 1,4,5-Trisphosphate / Q000378:metabolism; D007700:Kinetics; D008564:Membrane Potentials; D008856:Microscopy, Fluorescence; D009116:Muscarine / Q000494:pharmacology; D009538:Nicotine / Q000494:pharmacology; D011976:Receptors, Muscarinic / Q000187:drug effects / Q000502:physiology*; D011978:Receptors, Nicotinic / Q000187:drug effects / Q000502:physiology*; D013779:Tetrodotoxin / Q000494:pharmacology; D014407:Tumor Cells, Cultured
D015220:Calcium Channels; D011976:Receptors, Muscarinic; D011978:Receptors, Nicotinic; D002110:Caffeine; D013779:Tetrodotoxin; D009538:Nicotine; D001285:Atropine; D009116:Muscarine; D015544:Inositol 1,4,5-Trisphosphate; D000109:Acetylcholine; D002118:Calcium