Lack of effect of cADP-ribose and NAADP on the activity of skeletal muscleand heart ryanodine receptors

The calcium release channels/ryanodine receptors (RyRs) are potential/putat ive targets of cADPR (cyclic ADP-ribose) action in many tissue systems. In striated muscles, where RyRs predominate, cADPR action on these channels is controversial. Here cADPR modulation of cardiac and skeletal muscle RyR ch annels was tested. We considered factors reported as necessary for cADPR ac tion, such as the presence of calmodulin and/or FK binding proteins (FKBPs) . We found: 1) The RyR channel isoforms were insensitive to cADPR (or its m etabolite NAADP [nicotinic acid adenine dinucleotide phosphate]) under all conditions examined, as studied by: 1 a) single channel recordings in plana r lipid bilayers; 1b) macroscopic behavior of the RyRs in sarcoplasmic reti culum (SR) microsomes (including crude microsome preparations likely to ret ain putative cADPR cofactors) at room temperature and at 37 degreesC (net e nergized Ca2+ uptake or passive Ca2+ leak); 2) [P-32]cADPR did not bind sig nificantly to SR microsomes; 3) cADPR did not affect FKBP association to SR membranes. We conclude that cADPR does not interact directly with RyRs or RyR-associated SR proteins. Our results under in vitro conditions suggest t hat cADPR effects on Ca2+ signaling observed in vivo in mammalian striated muscle cells may reflect indirect modulation of RyRs or RyR-independent Ca2 + release systems. (C) 2001 Harcourt Publishers Ltd.