SARCOPLASMIC RETICULUM-ASSOCIATED AND PROTEIN-KINASE C-REGULATED ADP-RIBOSYL CYCLASE IN CARDIAC-MUSCLE

Two types of ADP-ribosyl cyclase activity were distinguished in dog an d rat cardiac muscles by measuring the enzymatic conversion of NGD (as an NAD analog) into the fluorescent product cyclic GDP-ribose in card iac muscle subcellular fractions. Both types of activity were confined to membrane fractions isolated from microsomes by sucrose gradient ce ntrifugation. One of the activities co-purified with fractions that we re enriched in sarcolemma (SLM), as evidenced by immunodetection of th e dihydropyridine receptor, while the other activity was found to co-p recipitate with the sarcoplasmic reticulum (SR), that was identified o n the basis of its immune-staining with a ryanodine receptor monoclona l antibody. In certain aspects, the plasma membrane-bound ADP-ribosyl cyclase activity resembled the characteristics of CD38 or CD38-like pr oteins: it was sensitive to thiols and lectins and was recognized by a monoclonal anti CD38 antibody. The SR enzyme had apparently distinct properties, as it was insensitive to both thiols and lectins and was n ot recognized by the CD38 antibody. In addition, the SR-associated ADP -ribosyl cyclase was inhibited by endogenous protein kinase C (PKC)-de pendent phosphorylation in both dog and rat cardiac SR. The PKC-modula ted SR ADP-ribosyl cyclase we describe here might be a principal compo nent of the signal transduction machinery that is responsible for regu lation of the intracellular levels of cADPR. (C) 1997 Academic Press.