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Ca2+-induced Ca2+ Release from Internal Stores in INS-1 Rat Insulinoma Cells

By Kyung Jin Choi, Dong Su Cho, Ju Young Kim, Byung Joon Kim, Kyung Moo Lee, Shin Hye Kim, Dong Kwan Kim, Se Hoon Kim and Hyung Seo Park


The secretion of insulin from pancreatic β-cells is triggered by the influx of Ca2+ through voltage-dependent Ca2+ channels. The resulting elevation of intracellular calcium ([Ca2+]i) triggers additional Ca2+ release from internal stores. Less well understood are the mechanisms involved in Ca2+ mobilization from internal stores after activation of Ca2+ influx. The mobilization process is known as calcium-induced calcium release (CICR). In this study, our goal was to investigate the existence of and the role of caffeine-sensitive ryanodine receptors (RyRs) in a rat pancreatic β-cell line, INS-1 cells. To measure cytosolic and stored Ca2+, respectively, cultured INS-1 cells were loaded with fura-2/AM or furaptra/AM. [Ca2+]i was repetitively increased by caffeine stimulation in normal Ca2+ buffer. However, peak [Ca2+]i was only observed after the first caffeine stimulation in Ca2+ free buffer and this increase was markedly blocked by ruthenium red, a RyR blocker. KCl-induced elevations in [Ca2+]i were reduced by pretreatment with ruthenium red, as well as by depletion of internal Ca2+ stores using cyclopiazonic acid (CPA) or caffeine. Caffeine-induced Ca2+ mobilization ceased after the internal stores were depleted by carbamylcholine (CCh) or CPA. In permeabilized INS-1 cells, Ca2+ release from internal stores was activated by caffeine, Ca2+, or ryanodine. Furthermore, ruthenium red completely blocked the CICR response in permeabilized cells. RyRs were widely distributed throughout the intracellular compartment of INS-1 cells. These results suggest that caffeine-sensitive RyRs exist and modulate the CICR response from internal stores in INS-1 pancreatic β-cells

Topics: Original Article
Publisher: The Korean Physiological Society and The Korean Society of Pharmacology
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Provided by: PubMed Central
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