Actin synthesis in cultured cardiac myocytes: comparative effects of doxorubicin, dactinomycin, and plicamycin.

Cultured neonatal rat myocardial cells (CMC) were incubated with 10(-8) to 10(-5) mol/L doxorubicin (ADR), dactinomycin (ACT), and plicamycin (MIT), respectively, in medium containing 35 mu Ci sulfur 35-labeled methionine to determine comparative effects on myocardial contractile protein synthesis. Cells were harvested in 2 mmol/L Tris buffer with 0.1% Triton X-100, homogenized, and fractionated by centrifugation. Aliquots of the extracts containing equivalent amounts of protein were applied to 8% to 15% gradient sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE). Similar aliquots were subjected to isoelectric focusing and to gel electrophoresis in the second dimension. All electrophoretic gels were autoradiographed. A concentration-dependent effect of ADR, ACT, and MIT on protein and on actin synthesis was found in cultured myocytes with decreased density of radiolabeled actin band in CMC exposed to either 10(-5) mol/L ADR, or from 10(-8) to 10(-5) mol/L ACT, or from 10(-7) to 10(-5) mol/L MIT. Autoradiographs of two-dimensional gels focused actin isoforms but showed substantial decreases of all actin isoforms in CMC extracts from 10(-7) mol/L ACT. ACT and MIT each decreased CMC protein synthesis by 20% at 10(-8) mol/L. At 10(-6) mol/L ADR, synthesis of alpha-actin was diminished preferentially compared with beta and gamma. Synthesis of all actin isoforms was diminished at 10(-5) mol/L ADR. The effect of MIT and ACT on CMC actin and protein synthesis in heart cells is not as specific as the effect of ADR on CMC actin and protein synthesis.