Spontaneous Ca2+ oscillations in subcellular compartments of vascular smooth muscle cells rely on different Ca2+ pools.
Spontaneous Ca2+ oscillations in vascular smooth muscle cells have been modeled using a single Ca2+ pool. This report describes spontaneous Ca2+ oscillations dependent on two separate Ca2+ sources for the nuclear versus cytoplasmic compartments. Changes in free intracellular Ca2+ were monitored with ratiometric Ca2+- fluorophores using confocal microscopy. On average, spontaneous oscillations developed in 79% of rat aortic smooth muscle cells that were synchronous between the cytoplasm and nucleus. Reduction of extracellular Ca2+ (less than 1 microM)decreased the frequency and amplitude of the cytoplasmic oscillations with 48% of the oscillations asynchronous between the nuclear and cytoplasmic compartments. Similar results were obtained with the Ca2+ channel blockers, nimodipine and diltiazem. Arg-vasopressin (AVP) induced a rapid release of intracellular Ca2+ stores that was greater in the nuclear compartment (4.20 +/- 0.23 ratio units, n = 56) than cytoplasm (2.54 +/- 0.28) in cells that had spontaneously developed prior oscillations. Conversely, cells in the same conditions lacking oscillations had a greater AVP-induced Ca2+ transient in the cytoplasm (4.99 +/- 0.66, n = 17) than in the nucleus (2.67 +/- 0.29). Pre-treatment with Ca2+ channel blockers depressed the AVP responses in both compartments with the cytoplasmic Ca2+ most diminished. Depletion of internal Ca2+ stores prior to AVP exposure blunted the nuclear response, mimicking the response of cells that lacked prior oscillations. Spontaneous oscillating cells had a greater sarcoplasmic reticulum network than cells that did not oscillate. We propose that spontaneous nuclear oscillations rely on perinuclear sarcoplasmic reticulum stores, while the cytoplasmic oscillations rely on Ca2+ influx.
Fedoryak
Olesya D
OD
Department of Physical Therapy, University of Kansas Medical Center, Kansas City, KS 66160, USA.
Searls
Yvonne
Y
Smirnova
Irina V
IV
Burns
Douglas M
DM
Stehno-Bittel
Lisa
L
D000818:Animals; D002118:Calcium / Q000502:physiology*; D020013:Calcium Signaling / Q000187:drug effects / Q000502:physiology*; D002451:Cell Compartmentation / Q000502:physiology*; D002478:Cells, Cultured; D009131:Muscle, Smooth, Vascular / Q000166:cytology / Q000502:physiology*; D009474:Neurons / Q000502:physiology; D051381:Rats; D012519:Sarcoplasmic Reticulum / Q000502:physiology; D013997:Time Factors; D014667:Vasopressins / Q000494:pharmacology
D014667:Vasopressins; D002118:Calcium