Cell growth-dependent expression of endothelin-1 provocable Ca2+ channels in cloned vascular smooth muscle cells.
To analyze the action of endothelin-1 (ET-1) on intracellular Ca ion ([Ca2+]i) handling, we have measured the [Ca2+]i transients in a cultured vascular smooth muscle cell (VSMC) line, A7r5, using two-dimensional microfluorophotometry. In the presence of 1 mM extracellular Ca2+ ([Ca2+]e), ET-1 (100 nM) induced a transient increase in [Ca2+]i due to Ca2+ release from sarcoplasmic reticulum and a subsequent sustained [Ca2+]i increase, suggestive of the entry via the voltage-dependent Ca2+ channel. The transient phase was heterogenous in the VSMC population; only two-thirds of VSMCs showed the phase, whereas all cells showed the sustained phase. To elucidate the cause of heterogeneity, we measured the [Ca2+]i using VSMCs cultured under two extreme conditions. When the cell cycle was arrested at the quiescent phase in the defined serum-free medium, the transient phase was observed in most cells. In contrast, when cell growth was promoted by the above medium plus PDGF (50 ng/ml), the [Ca2+]i response was completely abolished, whereas both the voltage-dependent Ca2+ channel and vasopressin-operated Ca2+ mobilization mechanism were universally preserved, irrespective of the culture conditions. These results may imply that the ET-1-mediated Ca2+ release mechanism is closely influenced by cell growth and preferentially effective at the quiescent phase.
Suzuki
T
T
Second Department of Internal Medicine, University of Tokyo, Japan.
Toyo-oka
T
T
Shin
W S
WS
Sugimoto
T
T
D002118:Calcium / Q000378:metabolism; D015220:Calcium Channels / Q000187:drug effects / Q000378:metabolism*; D002455:Cell Division / Q000187:drug effects / Q000502:physiology; D002460:Cell Line; D002999:Clone Cells; D016232:Endothelins / Q000494:pharmacology*; D007091:Image Processing, Computer-Assisted; D007700:Kinetics; D009131:Muscle, Smooth, Vascular / Q000166:cytology* / Q000187:drug effects / Q000378:metabolism; D010982:Platelet-Derived Growth Factor / Q000494:pharmacology; D011188:Potassium / Q000494:pharmacology; D014667:Vasopressins / Q000494:pharmacology
D015220:Calcium Channels; D016232:Endothelins; D010982:Platelet-Derived Growth Factor; D014667:Vasopressins; D011188:Potassium; D002118:Calcium