Figure 6. Effects of halothane on endogenous cyclic AMP-dependent protein phosphorylation in rat synaptosomal membranes. The membrane fraction from rat cerebrocortical synaptosomes was incubated under phosphorylating conditions in the absence of CaCl²for 60 s at 37 degrees C with [gamma-sup 32 p]ATP in the absence or presence of 2.4 vol% halothane as described in methods and materials. Protein phosphorylation was analyzed by sodium dodecyl sulfate/polyacrylamide gel electrophoresis followed by autoradiography. Lanes 1–4 contained 10 micro Meter PKI⁴-24, lanes 5–12 contained 10 micro Meter 8-bromo-cyclic AMP (8BrcA), and lanes 9–12 contained 10 micro Meter 8BrcA and 2 micro Meter okadaic acid (OA). The most prominent cyclic AMP-stimulated phosphoproteins are synapsin 1a, 1b, 2a, and 2b (M^r= 80,000, 75,000, 72,000, and 57,000, respectively; arrows). Halothane slightly potentiated the phosphorylation of several cyclic AMP-stimulated phosphoproteins (lanes 5–8), an effect that was prevented by the inclusion of OA (lanes 9–12), and inhibited the phosphorylation of a protein of M^r[approximately equal] 40,000 (lower arrow). The relative molecular weights (M^r) in kilodaltons (kDa) of protein standards are indicated on the left.