Developmental changes in the levels of substrates for cholera toxin-catalyzed and pertussis toxin-catalyzed ADP-ribosylation in rat cardiac cell membranes.

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Developmental changes in the substrates for cholera toxin (CTX)- and pertussis toxin (PTX)-catalyzed ADP-ribosylation in cardiac (ventricular) cell membranes were studied in fetal (16- to 20-day), neonatal (0- to 20-day) and adult (2- to 3-month) rats. The CTX and PTX substrates were determined by the method of CTX-catalyzed and PTX-catalyzed ADP-ribosylation of the α-subunit of GTP-binding (G) proteins, respectively. As early as fetal day 16, three substrates (45-, 47- and 52-kDa proteins) were identified for CTX-catalyzed ADP-ribosylation and one substrate (41-kDa protein) for PTX-catalyzed ADP-ribosylation. The levels of the three CTX substrates (fmol/mg tissue) increased with development between fetal day 16 and neonatal day 16, and then they decreased to their adult levels. The level of the one PTX substrate (fmol/mg tissue) changed as follows: the substrate decreased between fetal day 16 and the day of birth, increased abruptly for 4 days neonatal and increased slowly thereafter until neonatal day 16, and then decreased to the final adult level. The PTX substrate seems to reach a nearly maximum level earlier than the CTX substrates. This information is essential for understanding the developmental changes in the transmembrane signaling system between membrane receptors and their effectors which are coupled with the stimulatory and inhibitory G proteins.
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