Both the Ca2+-releasing mechanism induced by cyclic ADP-ribose (cADPR) and
the ADP-ribosyl cyclase (ADPRC) activity that converts NAD(+) to cADPR were
observed in a variety of cell types, We studied the ADPRC activity in rat
major salivary glands that include parotid gland (PG;), submandiblar gland
(SMG), and sublingual gland (SLG). The enzyme activity responsible for cADP
R synthesis was detected by spectrofluorometric assay using NGD(+) as a sub
strate. The enzyme activities in SLG, SMG,, and PG were about 400, 30, and
40 nmol/min/g tissue, respectively, in Ei-week-old rats, The highest value
was observed in SLG and this value was higher than those in other tissues;
e.g., spleen (200 nmol/min/g tissue). The enzyme activity in SLC: increased
gradually after birth and showed a maximum value at 3 weeks, On the other
hand, the enzyme activities almost did not change in both PG and SMG betwee
n 0 and 9 weeks, In spite of the high ADPRC activity in SLG:, we could not
detect the cADPR-induced Ca2+-release from SLG; microsomes. These results s
uggest that the ADPRC in SLG does not function through Ca2+-release observe
d in various tissues. (C) 2000 Academic Press.