passages.id: split_1_test_24_passage
passages.type: progene_text
passages.text: The regulation of intracellular free Ca2+ concentration ( [ Ca2+ ] i ) in B cells remains poorly understood and is presently explained almost solely by inositol 1,4,5-triphosphate ( IP3 ) - mediated Ca2+ release , followed by activation of a store - operated channel mechanism .