Activation of two different receptors mobilizes calcium from distinct stores in Xenopus oocytes.
Acetylcholine (ACh) and thyrotropin-releasing hormone (TRH) utilize inositol 1,4,5-trisphosphate (IP3) as a second messenger and evoke independent depolarizing membrane electrical responses accompanied by characteristic 45Ca efflux profiles in Xenopus laevis oocytes injected with GH3 pituitary cell mRNA. To determine whether this could be accounted for by mobilization of calcium from functionally separate stores, we measured simultaneously 45Ca efflux and membrane electrical responses to ACh and TRH in single oocytes. We found that depletion of ACh-sensitive calcium store did not affect the membrane electrical response to TRH and the TRH-evoked 45Ca efflux. Our data suggest that ACh and TRH mobilize calcium from distinct cellular stores in the oocyte. This is the first demonstration in a single cell of strict subcellular compartmentalization of calcium stores coupled to two different populations of cell membrane receptors that utilize the same second messenger.
Shapira
H
H
Division of Physiology and Pharmacology, Sackler Faculty of Medicine, Tel Aviv University, Ramat Aviv, Israel.
Lupu-Meiri
M
M
Gershengorn
M C
MC
Oron
Y
Y
D000109:Acetylcholine / Q000494:pharmacology*; D000818:Animals; D002118:Calcium / Q000378:metabolism*; D002132:Calcium Radioisotopes; D002460:Cell Line; D002462:Cell Membrane / Q000187:drug effects / Q000502:physiology; D005260:Female; D066298:In Vitro Techniques; D007700:Kinetics; D008564:Membrane Potentials / Q000187:drug effects; D008845:Microinjections; D009865:Oocytes / Q000187:drug effects / Q000502:physiology*; D010911:Pituitary Neoplasms; D012333:RNA, Messenger / Q000008:administration & dosage / Q000235:genetics; D012334:RNA, Neoplasm / Q000008:administration & dosage / Q000235:genetics; D011950:Receptors, Cholinergic / Q000502:physiology*; D017981:Receptors, Neurotransmitter / Q000235:genetics / Q000502:physiology*; D018025:Receptors, Thyrotropin-Releasing Hormone; D013973:Thyrotropin-Releasing Hormone / Q000378:metabolism / Q000494:pharmacology*; D014982:Xenopus laevis
D002132:Calcium Radioisotopes; D012333:RNA, Messenger; D012334:RNA, Neoplasm; D011950:Receptors, Cholinergic; D017981:Receptors, Neurotransmitter; D018025:Receptors, Thyrotropin-Releasing Hormone; D013973:Thyrotropin-Releasing Hormone; D000109:Acetylcholine; D002118:Calcium