RELEASE-ACTIVATED CA2-GANGLIA( TRANSPORT IN NEURONS OF FROG SYMPATHETIC)

Frog sympathetic ganglion neurons exhibit a novel Ca2+ uptake mechanis m, release-activated calcium transport or RACT, which is manifest in b oth cytosolic and store [Ca2+] signals as greatly accelerated Ca2+ upt ake after Ca2+ release from internal stores. RACT is activated by Ca2 release but not by Ca2+ entry and serves to selectively refill Ca2+ s tores after release. RACT lowers cytosolic [Ca2+] with a rate constant about 1.6 times that of the SERCA pump with empty ER. RACT is thapsig argin-insensitive, was eliminated by ryanodine, but was not affected b y blocking mitochondrial or plasma membrane Ca2+ transport. A Ca2+ flu x model with RACT in the ER membrane reproduced the cytosolic and stor e [Ca2+] responses to all stimuli.