Partial inhibition of SERCA is responsible for extracellular Ca2+ dependence of AlF-4-induced [Ca2+]i oscillations in rat pancreatic |
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Authors: | Chong Seon Ah Hong Soo Young Moon Seok Jun Park Jee Won Hong Jeong-Hee An Jeong Mi Lee Syng-Ill Shin Dong Min Seo Jeong Taeg |
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Institution: | Department of Oral Biology, Yonsei University College of Dentistry, Shinchon-dong 134, Seodaemun-gu, Seoul 120-752, Korea. |
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Abstract: | AlF4-is known to generate oscillations in intracellular Ca2+ concentration (Ca2+]i) by activating G proteins in many cell types. However, in rat pancreatic acinar cells, AlF4--evoked Ca2+]i oscillations were reported to be dependent on extracellular Ca2+, which contrasts with the Ca2+]i oscillations induced by cholecystokinin (CCK). Therefore, we investigated the mechanisms by which AlF4- generates extracellular Ca2+-dependent Ca2+]i oscillations in rat pancreatic acinar cells. AlF4--induced Ca2+]i oscillations were stopped rapidly by the removal of extracellular Ca2+ and were abolished on the addition of 20 mM caffeine and 2 µM thapsigargin, indicating that Ca2+ influx plays a crucial role in maintenance of the oscillations and that an inositol 1,4,5-trisphosphate-sensitive Ca2+ store is also required. The amount of Ca2+ in the intracellular Ca2+ store was decreased as the AlF4--induced Ca2+]i oscillations continued. Measurement of 45Ca2+ influx into isolated microsomes revealed that AlF4-directly inhibited sarco/endoplasmic reticulum Ca2+-ATPase (SERCA). The activity of plasma membrane Ca2+-ATPase during AlF4- stimulation was not significantly different from that during CCK stimulation. After partial inhibition of SERCA with 1 nM thapsigargin, 20 pM CCK-evoked Ca2+]i oscillations were dependent on extracellular Ca2+. This study shows that AlF4- induces Ca2+]i oscillations, probably by inositol 1,4,5-trisphosphate production via G protein activation but that these oscillations are strongly dependent on extracellular Ca2+ as a result of the partial inhibition of SERCA. cholecystokinin; plasma membrane adenosine 5'-triphosphatase; G proteins; caffeine |
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