ATP-induced activation of expressed RyR3 at low free calcium

Ca2+ channel properties of the mink ryanodine receptor type 3 (RVR3), expre ssed in HEK293 cells, were studied in planar lipid bilayers to which RyR3 r ich membrane fragments had been fused, RyR3 channels were not active at res ting levels of Ca-free(2+) but were gated by an additional 1 mM ATP, exhibi ting long open times, The second major finding was the absence of channel i nactivation at millimolar Ca-free(2+). Insertion of a myc tag at the N-term inus of RyR3 did not affect the channel properties, As to skeletal muscle, the observed type 3 channel properties appear physiologically meaningful by assisting type 1 channels in calcium release. (C) 2000 Federation of Europ ean Biochemical Societies.