ADP-ribosyl cyclase in rat salivary glands

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.