Agonist-activated, ryanodine-sensitive, IP3-insensitive Ca2+ release channels in longitudinal muscle of intestine

Abstract

We have previously shown that Ca2+ mobilization in longitudinal muscle is not mediated by inositol 1,4,5-trisphosphate (IP3) and depends on an obligatory influx of Ca2+. The present study examined whether Ca2+ influx activates ryanodine-sensitive Ca2+ channels to cause Ca(2+)-induced Ca2+ release. Ryanodine bound with high affinity to longitudinal muscle cells [dissociation constant (Kd) 7.3 +/- 0.3 nM] and microsomes (Kd 7.5 +/- 0.4 nM) and induced concentration-dependent 45Ca2+ efflux [50% effective concentration (EC50) 1.3 +/- 0.5 nM], increase in cytosolic free Ca2+ (EC50 2.0 +/- 0.7 nM), and contraction (EC50 0.9 +/- 0.2 nM) but had no effect in circular muscle cells. Ryanodine binding and ryanodine-induced Ca2+ release were enhanced by caffeine and inhibited by dantrolene and ruthenium red but were not affected by IP3 or heparin. Changes in Ca2+ concentration (50-500 nM) caused Ca2+ release from permeabilized longitudinal but not circular muscle cells loaded with 45Ca2+. The contractile agonist cholecystokinin-8 elicited 45Ca2+ efflux in both circular and longitudinal muscle cells; efflux in longitudinal muscle cells was abolished by Ca2+ channel blockers and by pretreatment of the cells with ryanodine. Pretreatment with thapsigargin abolished agonist-induced 45Ca2+ efflux in both cell types. We conclude that ryanodine-sensitive IP3-insensitive Ca2+ release channels with properties similar to those in cardiac muscle are present in longitudinal but not circular muscle cells of intestine and that agonist-mediated Ca2+ influx activates these channels, leading to Ca(2+)-induced Ca2+ release.

Hypercontractility of Intestinal Longitudinal Smooth Muscle Induced by Cytokines Is Mediated by the Nuclear Factor-κB/AMP-Activated Kinase/Myosin Light Chain Kinase Pathway

“…In longitudinal muscle cells, as previously noted herein, agonist-mediated activation of cPLA 2 and generation of arachidonic acid are the triggers for Ca 21 mobilization and initial muscle contraction (Murthy et al, 1991(Murthy et al, , 1995Kuemmerle et al, 1994Kuemmerle et al, , 1998. Previous studies had shown that both cAMP-and cGMP-dependent protein kinases phosphorylate cPLA 2 and inhibit Ca 21 mobilization and contraction , in contrast to the augmentation of contraction induced by the catalytic subunit of PKA on release from binding to IkBa.…”

“…-and cyclic ADP ribose-induced Ca 21 release via ryanodine receptors/Ca 21 channels (Murthy et al, 1991(Murthy et al, , 1995Kuemmerle et al, 1994Kuemmerle et al, , 1998Murthy, 2006). There is minimal participation of G q , RGS4, and IP 3 -dependent Ca 21 release in this muscle.…”

“…In intestinal longitudinal smooth muscle, however, there is minimal participation of G q , RGS4, and IP 3 -dependent Ca 21 release (Murthy et al, 1991(Murthy et al, , 1995Kuemmerle et al, 1994Kuemmerle et al, , 1998Murthy, 2006 release via ryanodine receptors (Kuemmerle et al, 1994). Initial contraction is terminated, in part, by SERCA2-mediated Ca 21 uptake into Ca 21 stores.…”

Pharmacological Modulation of Sarcoplasmic Reticulum Function in Smooth Muscle

“…Only InsP 3 R1 is known to undergo alternative splicing with two segments (Yoshida and Imai, 1997): the 15-residue-long S1 segment located in the ligand-binding domain predominantly expressed in peripheral tissues and the 40-residue long S2 segment located in the coupling domain and predominantly expressed in the nervous system. As is the case for the majority of cell types examined so far (Wilcox et al, 1993(Wilcox et al, , 1998, smooth muscle cells express multiple InsP 3 R isoforms, although some could express none, such as the longitudinal intestinal smooth muscle cells (Kuemmerle et al, 1994).…”

Jun kinase-induced overexpression of leukemia-associated Rho GEF (LARG) mediates sustained hypercontraction of longitudinal smooth muscle in inflammation

“…Ca 2ϩ mobilization in longitudinal muscle is mediated by activation of cytosolic phospholipase A 2 (cPLA 2 ) and generation of arachidonic acid (AA), leading to Ca 2ϩ influx and stimulation of cyclic ADP ribose (cADPR) (30,31,39). Ca 2ϩ and cADPR act in concert to induce Ca 2ϩ release via ryanodine receptors (RYR2)/Ca 2ϩ channels (29).…”