Recent studies have provided evidence for a role of cyclic ADP-ribose (cADPR) in the regulation of intracellular calcium in smooth muscles of the intestine, blood vessels and airways. We investigated the presence and subcellular localization of ADP-ribosyl cyclase, the enzyme that catalyzes the conversion of β-NAD+ to cADPR, and cADPR hydrolase, the enzyme that degrades cADPR to ADPR, in tracheal smooth muscle (TSM). Sucrose density fractionation of TSM crude membranes provided evidence that ADP-ribosyl cyclase and cADPR hydrolase activities were associated with a fraction enriched in 5'-nucleotidase activity, a plasma membrane marker enzyme, but not in a fraction enriched in either sarcoplasmic endoplasmic reticulum calcium ATPase or ryanodine receptor channels, both sarcoplasmic reticulum markers. The ADP-ribosyl cyclase and cADPR hydrolase activities comigrated at a molecular weight of approximately 40 kDa on SDS-PAGE. This comigration was confirmed by gel filtration chromatography. Investigation of kinetics yielded K(m) values of 30.4 ± 1.5 and 695.3 ± 171.2 μM and V(max) values of 330.4 ± 90 and 102.8 ± 17.1 nmol/mg/h for ADP-ribosyl cyclase and cADPR hydrolase, respectively. These results suggest a possible role for cADPR as an endogenous modulator of [Ca2+](i) in porcine TSM cells. (C) 2000 Elsevier Science B.V.
|Original language||English (US)|
|Number of pages||8|
|Journal||Biochimica et Biophysica Acta - Molecular Cell Research|
|State||Published - Oct 20 2000|
Bibliographical noteFunding Information:
This work was supported by Grants from National Institutes of Health (HL057498 to M.S.K., DA11806 to T.F.W. and GM56686 to G.C.S.).
- ADP-ribosyl cyclase
- Airway smooth muscle
- Cyclic ADP-ribose
- Cyclic ADP-ribose hydrolase