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

• Published in: The Korean journal of physiology & pharmacology Vol. 15; no. 1; pp. 53 - 59
• Main Authors: Choi, Kyung Jin, Cho, Dong Su, Kim, Ju Young, Kim, Byung Joon, Lee, Kyung Moo, Kim, Shin Hye, Kim, Dong Kwan, Kim, Se Hoon, Park, Hyung Seo
• Format: Journal Article
• Language: English
• Published: The Korean Physiological Society and The Korean Society of Pharmacology 01.02.2011
• Subjects: Original
• ISSN: 1226-4512; 2093-3827
• DOI: 10.4196/kjpp.2011.15.1.53

The secretion of insulin from pancreatic β-cells is triggered by the influx of Ca 2+ through voltage-dependent Ca 2+ channels. The resulting elevation of intracellular calcium ([Ca 2+ ] i ) triggers additional Ca 2+ release from internal stores. Less well understood are the mechanisms involved in Ca 2+ mobilization from internal stores after activation of Ca 2+ 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 Ca 2+ , respectively, cultured INS-1 cells were loaded with fura-2/AM or furaptra/AM. [Ca 2+ ] i was repetitively increased by caffeine stimulation in normal Ca 2+ buffer. However, peak [Ca 2+ ] i was only observed after the first caffeine stimulation in Ca 2+ free buffer and this increase was markedly blocked by ruthenium red, a RyR blocker. KCl-induced elevations in [Ca 2+ ] i were reduced by pretreatment with ruthenium red, as well as by depletion of internal Ca 2+ stores using cyclopiazonic acid (CPA) or caffeine. Caffeine-induced Ca 2+ mobilization ceased after the internal stores were depleted by carbamylcholine (CCh) or CPA. In permeabilized INS-1 cells, Ca 2+ release from internal stores was activated by caffeine, Ca 2+ , 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.