DIFFERENTIAL-EFFECTS OF THE M(1)-M(5) MUSCARINIC ACETYLCHOLINE-RECEPTOR SUBTYPES ON INTRACELLULAR CALCIUM AND ON THE INCORPORATION OF CHOLINE INTO MEMBRANE-LIPIDS IN GENETICALLY-MODIFIED CHINESE-HAMSTER OVARY CELL-LINES

We compared responses of Chinese hamster ovary (CHO) cell lines stably transfected with human genes for the M(1)-M(5) muscarinic receptor su btypes to several stimuli. While ATP brought about similar increases i n the concentration of intracellular Ca2+ ions ([Ca2+](i)) in the cell lines expressing all individual receptor subtypes, carbachol acted wi th much higher potency and efficacy on the cells expressing the M(1), M(3), and M(5) receptor subtypes than on those expressing the M(2) and M(4) subtypes. The maximum [Ca2+](I) responses to ATP corresponded to 41-75% of the maximum responses to carbachol in the cells expressing the M(1), M(3), and M(5) receptor subtypes. The responses to ATP were strongly suppressed (>75% decrease) by a preliminary administration of a maximally active concentration of carbachol in these three cell lin es, whereas the responses to carbachol were less sensitive to the prel iminary administration of a maximally active concentration of ATP (<25 % decrease), It appears likely that carbachol and ATP release Ca2+ ion s from identical intracellular stores, Tetradecanoylphorbol acetate (T PA) strongly inhibited the responses of [Ca2+](i) to both carbachol an d ATP and enhanced the incorporation of [C-14]choline into lipids in a ll five CHO cell lines investigated, On the other hand, the incorporat ion of [C-14]choline into lipids was diminished by carbachol in the ce ll line expressing the M(3) receptor subtype and unchanged in the othe r cell lines, This effect of carbachol was not dependent on the presen ce of extracellular Ca2+ ions and was not affected by TPA, which dimin ished the response of [Ca2+](i) to muscarinic stimulation. It is sugge sted that it was due to muscarinic receptor-mediated activation of pho spholipase D. Copyright (C) 1997 Elsevier Science Inc.