Growth-dependent alterations of intracellular Ca(2+)-handling mechanisms of vascular smooth muscle cells. PDGF negatively regulates functional expression of voltage-dependent, IP3-mediated, and CA(2+)-induced Ca2+ release channels.
To examine the alterations of intracellular Ca2+ ([Ca2+]i)-handling mechanisms in cultured vascular smooth muscle cells (VSMCs) of rat aorta (Shin et al Circ Res 1991;69:551-556), we stimulated VSMCs by extracellular high K+, caffeine, and angiotensin II and evaluated Ca2+ influx through voltage-dependent Ca2+ channels, Ca(2+)-induced Ca2+ release, and inositol trisphosphate-dependent Ca2+ release from internal stores. Percentage of VSMCs responding to each stimulant (responder ratio) and degree of [Ca2+]i increase in the responding cells were analyzed by a two-dimensional fura-2 imaging system. The responder ratios to the three stimulants were high (70-90%) in the quiescent phase (days 1-2), although some cells selectively responded to one or two of the stimulants. Responder ratios prominently decreased to approximately 20% in the proliferating phase (days 2.5-3). In the subconfluent (days 3.5-4) and postconfluent (days 5-6) phases, the responder ratio to high K+ and angiotensin II recovered to the same level as during the quiescent phase, whereas that to caffeine remained low (approximately 10-20%). In responding cells, the degree of [Ca2+]i increase by caffeine and angiotensin II was stable (approximately 100%) during culturing, whereas that to high K+ was small (approximately 30-40%) in the quiescent and proliferating phases and rapidly increased threefold in the subconfluent and postconfluent phases. Furthermore, arrest of cell growth in serum-free medium prevented the reduction of responder ratios in the proliferating phase and restored the decreased ratio of the caffeine responder. Acceleration of VSMC proliferation by platelet-derived growth factor decreased the ratios in all phases. These results imply that 1) the functional expressions of [Ca2+]i-handling mechanisms in response to these vasoactive stimuli are influenced by cell growth and cytodifferentiation of VSMCs or platelet-derived growth factor and 2) they are regulated independently from each other.
Masuo
M
M
Second Department of Internal Medicine, Faculty of Medicine, University of Tokyo, Japan.
Toyo-oka
T
T
Shin
W S
WS
Sugimoto
T
T
D000804:Angiotensin II / Q000494:pharmacology; D000818:Animals; D002110:Caffeine / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism* / Q000502:physiology; D015220:Calcium Channels / Q000378:metabolism* / Q000502:physiology; D002478:Cells, Cultured; D004594:Electrophysiology; D015544:Inositol 1,4,5-Trisphosphate / Q000502:physiology*; D007425:Intracellular Membranes / Q000378:metabolism*; D009131:Muscle, Smooth, Vascular / Q000166:cytology / Q000378:metabolism*; D010982:Platelet-Derived Growth Factor / Q000502:physiology*; D011188:Potassium / Q000494:pharmacology
D015220:Calcium Channels; D010982:Platelet-Derived Growth Factor; D000804:Angiotensin II; D002110:Caffeine; D015544:Inositol 1,4,5-Trisphosphate; D011188:Potassium; D002118:Calcium