TABLE 1

Gαi-mediated carbachol-dependent inhibition of isoproterenol-stimulated cAMP accumulation in neonatal and adult cardiomyocytes

Neonatal or adult cardiomyocytes were pretreated for 24 h at 37° C with vehicle or PTX (100 ng/ml for neonate and 1 μg/ml for adult). Incubations were for 5 min at room temperature in the absence or presence of isoproterenol (10-7 M) or carbachol (10-5 M, alone or starting 5 min before isoproterenol). cAMP was extracted from cells and measured by radioimmunoassay as described under Materials and Methods. Results are presented as mean ± S.E.M. (n = 6).
Neonate Adult
-PTX +PTX -PTX +PTX
pmol/dish pmol/100,000 cells
Basal 10 ± 5 13 ± 8 12 ± 6 15 ± 7
Carbachol 9 ± 4 11 ± 6 9 ± 6 10 ± 5
Isoproterenol 268 ± 24* 261 ± 30* 333 ± 42* 329 ± 34*
Isoproterenol + Carbachol 73 ± 11*† 241 ± 19* 93 ± 12*† 284 ± 31*

  • ↵* P < 0.05 versus corresponding basal.

  • ↵† P < 0.05 versus corresponding isoproterenol.