title: Ca-induced Ca Release from Internal Stores in INS-1 Rat Insulinoma Cells.
abstract: 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.
authors: Department of Physiology, College of Medicine, Konyang University, Daejeon 302-718, Korea.
authors: Kyung Jin
authors: KJ
authors: Choi
authors: Dong Su
authors: DS
authors: Cho
authors: Ju Young
authors: JY
authors: Kim
authors: Byung Joon
authors: BJ
authors: Kim
authors: Kyung Moo
authors: KM
authors: Lee
authors: Shin Hye
authors: SH
authors: Kim
authors: Dong Kwan
authors: DK
authors: Kim
authors: Se Hoon
authors: SH
authors: Kim
authors: Hyung Seo
authors: HS
authors: Park