Sphingomyelinase treatment inhibits contraction response of rat thoracic aortae to phorbol ester

Ceramide has been shown to inhibit protein kinase activity in various systems by inhibiting translocation to the cell membrane. Previous studies have shown that treatment of vascular smooth muscle cells with sphingomyelinase (SMase; 0.1 U/ml) results in a 15-fold increase in intracellular ceramide levels. We tested the hypothesis that incubation of aortic ring segments with SMase would result in an attenuation in the contraction response to phorbol ester. Thoracic aortae from male Sprague Dawley rats were harvested and mounted in a muscle bath for isometric recording. Rings were incubated with or without 0.1 U/ml SMase for 30 min before the contraction response to phorbol dibutyrate (PDBu; 0-10^-6M) was determined. We observed a rightward shift in the contraction response curve to PDBu in rings incubated with SMase when compared to control rings. We conclude that SMase incubation decreases the sensitivity of aortic ring segments to phorbol ester, possibly through ceramide-mediated inhibition of PKC.