Imaging of intracellular calcium stores in single permeabilized lens cells

Intracellular Ca2+ stores in permeabilized sheep lens cells were imaged wit h mag-fura 2 to characterize their distribution and sensitivity to Ca2+-rel easing agents. Inositol 1,4,5-trisphosphate (IP3) or cyclic ADP-ribose (cAD PR) released Ca2+ from intracellular Ca2+ stores that were maintained by an ATP-dependent Ca2+ pump. The IP3 antagonist heparin inhibited IP3- but not cADPR-mediated Ca2+ release, whereas the cADPR antagonist 8-amino-cADPR in hibited cADPR- but not IP3-mediated Ca2+ release, indicating that IP3 and c ADPR were operating through separate mechanisms. A Ca2+ store sensitive to IP3, cADPR, and thapsigargin appeared to be distributed throughout all intr acellular regions. In some cells a Ca2+ store insensitive to IP3, cADPR, th apsigargin, and 2,4-dinitrophenol, but not ionomycin, was present in a juxt anuclear region. We conclude that lens cells contain intracellular Ca2+ sto res that are sensitive to IP3, cADPR, and thapsigargin, as well as a Ca2+ s tore that appears insensitive to all these agents.