Induction of Ca2+ oscillations by vasopressin in the presence of tetraethylammonium chloride in cultured vascular smooth muscle cells.
The change of cytosolic Ca2+ concentration ([Ca2+]i) caused by vasopressin was examined in indo-1-loaded A7r5 smooth muscle cells by use of the high-performance laser cytometer and ratiometric fluorescence method. Vasopressin (100 nM) caused an initial rapid rise and a delayed increase in [Ca2+]i (n = 6). However, in the presence of tetraethylammonium chloride (10 mM), vasopressin consistently triggered sustained Ca2+ oscillations which were preceded by a large peak of [Ca2+]i. The latency for the development of this huge increase in [Ca2+]i prior to the occurrence of sustained Ca2+ oscillations was always the same. The frequency and amplitude of this type of Ca2+ oscillation varied depending upon the extracellular Ca2+ concentration. Ca(2+)-free solution did not completely suppress the sustained Ca2+ oscillations, but caffeine (20 mM) effectively abolished them. The present findings indicate that in A7r5 smooth muscle cells, the sustained Ca2+ oscillations triggered by vasopressin in the presence of tetraethylammonium chloride were mainly due to Ca2+ release from IP3-sensitive Ca2+ stores and Ca2+ influx from extracellular space, and did not require the pacemaker activity derived from the surface membrane. Moreover, the vasopressin-induced change in [Ca2+]i appeared to be linked to pertussis toxin-insensitive GTP-binding protein(s).
Wu
S N
SN
Department of Physiology, Kaohsiung Medical College, Taiwan.
Yu
H S
HS
Seyama
Y
Y
D000818:Animals; D001013:Aorta, Thoracic / Q000187:drug effects / Q000378:metabolism; D002110:Caffeine / Q000494:pharmacology*; D002118:Calcium / Q000378:metabolism*; D002999:Clone Cells; D004347:Drug Interactions; D005110:Extracellular Space / Q000502:physiology; D005456:Fluorescent Dyes; D019204:GTP-Binding Proteins / Q000378:metabolism; D007211:Indoles; D007700:Kinetics; D009131:Muscle, Smooth, Vascular / Q000187:drug effects / Q000378:metabolism*; D009991:Oscillometry; D037342:Pertussis Toxin; D051381:Rats; D013050:Spectrometry, Fluorescence; D019789:Tetraethylammonium; D013757:Tetraethylammonium Compounds / Q000494:pharmacology*; D013997:Time Factors; D014667:Vasopressins / Q000494:pharmacology*; D010566:Virulence Factors, Bordetella / Q000494:pharmacology
D005456:Fluorescent Dyes; D007211:Indoles; D013757:Tetraethylammonium Compounds; D010566:Virulence Factors, Bordetella; D014667:Vasopressins; D002110:Caffeine; D019789:Tetraethylammonium; D037342:Pertussis Toxin; D019204:GTP-Binding Proteins; C048960:indo-1; D002118:Calcium