Cell Calcium (2008) 44, 180—189 journal homepage: www.elsevier.com/locate/ceca Full length ryanodine receptor subtype 3 encodes spontaneous calcium oscillations in native duodenal smooth muscle cells Fabrice Dabertrand, Jean Mironneau, Nathalie Macrez, Jean-Luc Morel * Centre de Neurosciences Int´ egratives et Cognitives, CNRS UMR5228, Universit´ es de Bordeaux, avenue des facult´ es, 33405 Talence, France Received 8 August 2007; received in revised form 12 September 2007; accepted 4 November 2007 Available online 18 January 2008 This work is dedicated to J.L. Lavie who died in August 2006. KEYWORDS Ryanodine receptor; Calcium oscillations; RYR3; Alternative splicing; RYR2; Smooth muscle; Duodenum Summary Two isoforms of the ryanodine receptor subtype 3 (RYR3) have been described in smooth muscle. The RYR3 short isoform (RYR3S) negatively regulates the calcium-induced calcium release mechanism encoded by the RYR2, whereas the role of the full length isoform of RYR3 (RYR3L) was still unclear. Here, we describe RYR-dependent spontaneous Ca 2+ oscillations measured in 10% of native duodenum myocytes. We investigated the role of RYR3 isoforms in these spontaneous Ca 2+ signals. Inhibition of RYR3S expression by antisense oligonucleotides revealed that both RYR2 and RYR3L were able to propagate spontaneous Ca 2+ waves that were distinguishable by frequency analysis. When RYR3L expression was inhibited, the spontaneous Ca 2+ oscillations were never observed, indicating that RYR3S inhibited the function of RYR2. RYR2 expression inhibition led to Ca 2+ oscillations identical to those observed in control cells suggesting that RYR3S did not functionally interact with RYR3L. The presence and frequency of RYR3L-dependent Ca 2+ oscillations were dependent on sarcoplasmic reticulum Ca 2+ content as revealed by long-term changes of the extracellular Ca 2+ concentration. Our study shows that, in native duodenal myocytes, the spontaneous Ca 2+ waves are encoded by the RYR3L alone, which activity is regulated by sarcoplasmic reticulum Ca 2+ loading. © 2007 Elsevier Ltd. All rights reserved. Abbreviations: RYR, ryanodine receptor; RYR3S, RYR3 short isoform; RYR3L, full length RYR3 isoform; SR, sarcoplasmic reticulum; InsP3R, inositol 1,4,5-trisphosphate receptor; CICR, Ca 2+ -induced Ca 2+ release; [Ca 2+ ] i , intracellular Ca 2+ concentration; ICC, intersticial Cajal cells; fluo-4-AM, fluo-4-acetoxymethylester; ACh, acetylcholine; SERCA, sarcoendoplasmic reticulum Ca 2+ ATPase; TRPC, transient receptor potential channel; ROI, region of interest; asSCR, scrambled antisense oligonucleotide. ∗ Corresponding author. Tel.: +33 5 4000 8886; fax: +33 5 4000 2561. E-mail address: jl.morel@cnic.u-bordeaux1.fr (J.-L. Morel). 0143-4160/$ — see front matter © 2007 Elsevier Ltd. All rights reserved. doi:10.1016/j.ceca.2007.11.009