Muscarinic acetylcholine receptors stimulate Ca2+ influx in PC12D cells predominantly via activation of Ca2+ store-operated channels.
Activation of muscarinic acetylcholine receptors (mAChRs) causes the rapid release of Ca2+ from intracellular stores and a sustained influx of external Ca2+ in PC12D cells, a subline of the widely studied cell line PC12. Release of Ca2+ from intracellular stores and a sustained influx of Ca2+ are also observed following exposure to thapsigargin, a sesquiterpene lactone that depletes intracellular Ca2+ pools by irreversibly inhibiting the Ca2+ pump of the endoplasmic reticulum. In this study, we show that carbachol and thapsigargin empty the same intracellular Ca2+ stores, and that these stores are a subset of intracellular stores depleted by the Ca2+ ionophore ionomycin. Intracellular Ca2+ stores remain depleted during continuous stimulation of mAChR with carbachol in medium containing 2 mM extracellular Ca2+, but rapidly refill following inhibition of mAChRs with atropine. Addition of atropine to carbachol-stimulated cells causes intracellular Ca2+ levels to return to baseline levels in two steps: a rapid decrease that correlates with the reuptake of Ca2+ into internal stores and a delayed decrease that correlates with the inhibition of a Mn2+-permeable Ca2+ channel. Several lines of evidence suggest that carbachol and thapsigargin stimulate Ca2+ influx by a common mechanism: (i) pretreatment with thapsigargin occludes atropine-mediated inhibition of Ca2+ influx, (ii) carbachol and thapsigargin applied individually or together are equally efficient at stimulating the influx of Mn2+, and (iii) identical rates of Ca2+ influx are observed when Ca2+ is added to cells pretreated with carbachol, thapsigargin, or both agents in the absence of extracellular Ca2+. Taken together, these data suggest that the sustained influx of extracellular Ca2+ observed following activation of mAChRs in PC12D cells is mediated primarily by activation of a Mn2+-permeable, Ca2+ store-operated Ca2+ channel.
Department of Neurochemistry, Faculty of Medicine, University of Tokyo, Hongo 7-3-1, Bunkyo-ku, Tokyo 113-0033.
Tatsuhiko
T
Ebihara
Feifan
F
Guo
Lei
L
Zhang
Ju Young
JY
Kim
David
D
Saffen
D000818:Animals; D002118:Calcium / Q000378:metabolism*; D015640:Ion Channel Gating / Q000502:physiology*; D007473:Ion Channels / Q000378:metabolism*; D016716:PC12 Cells; D051381:Rats; D011976:Receptors, Muscarinic / Q000502:physiology*
D007473:Ion Channels; D011976:Receptors, Muscarinic; D002118:Calcium