Mechanisms of subcellular cytosolic Ca2+ signaling evoked by stimulation of the vasopressin V1a receptor.
Receptor activation may result in distinct subcellular patterns of Ca2+ release. To define the subcellular distribution of Ca2+i signals induced by stimulation of the vasopressin V1a receptor, we expressed the cloned receptor in Xenopus oocytes. Oocytes were then loaded with fluo-3 and observed using confocal microscopy. Vasopressin induced a single concentric wave of increased Ca2+ that radiated inward from the plasma membrane. With submaximal stimulation, however, regions of the Ca2+ wave spontaneously reorganized into repetitive (oscillatory) waves. Focal stimulation of a small part of the plasma membrane resulted in a Ca2+ wave which began at the point of stimulation, radiated toward the center of the cell, then reorganized into multiple foci of repetitive, colliding waves and spirals of increased Ca2+i. The pattern of Ca2+ signaling induced by focal or global stimulation was not altered in Ca(2+)-free medium, although signals did not propagate as fast. Finally, subcellular Ca2+ signaling patterns induced by vasopressin were inhibited by caffeine, while neither vasopressin nor microinjection of inositol trisphosphate blocked caffeine-induced increases in cytosolic Ca2+. Thus, stimulation of the V1a receptor in this cell system induces a complex pattern of Ca2+ signaling which is influenced by (1) the magnitude of the stimulus, (2) the distribution of the surface receptors that are stimulated, and (3) mobilization of Ca2+ from the extracellular space as well as from two distinct endogenous Ca2+ pools. The manner in which a single type of receptor is activated may represent an important potential mechanism for subcellular Ca2+i signaling.
Nathanson
M H
MH
Liver Center, Yale University School of Medicine, New Haven, Connecticut 06510.
Moyer
M S
MS
Burgstahler
A D
AD
O'Carroll
A M
AM
Brownstein
M J
MJ
Lolait
S J
SJ
D000818:Animals; D001127:Arginine Vasopressin / Q000378:metabolism / Q000494:pharmacology*; D002110:Caffeine / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism*; D002462:Cell Membrane / Q000187:drug effects / Q000502:physiology; D003001:Cloning, Molecular; D003600:Cytosol / Q000378:metabolism; D005260:Female; D066298:In Vitro Techniques; D015544:Inositol 1,4,5-Trisphosphate / Q000494:pharmacology; D015759:Ionomycin / Q000494:pharmacology; D007700:Kinetics; D008856:Microscopy, Fluorescence; D009865:Oocytes / Q000187:drug effects / Q000502:physiology*; D017483:Receptors, Vasopressin / Q000187:drug effects / Q000235:genetics / Q000502:physiology*; D011994:Recombinant Proteins / Q000187:drug effects / Q000378:metabolism; D015398:Signal Transduction; D013997:Time Factors; D014981:Xenopus
D017483:Receptors, Vasopressin; D011994:Recombinant Proteins; D001127:Arginine Vasopressin; D002110:Caffeine; D015759:Ionomycin; D015544:Inositol 1,4,5-Trisphosphate; D002118:Calcium