An improved permeabilization protocol for the introduction of peptides into cardiac myocytes: Application to protein kinase C research

We have developed an improved, less disruptive procedure for the transient permeabilization of neonatal cardiac myocytes using saponin. The method allows delivery of peptides to a high percentage of cells in culture without effects on long-term cell viability. Permeation was confirmed microscopically by cellular uptake of a fluorescently labeled peptide and biochemically by uptake of ¹²⁵I-labeled calmodulin and a 20-kD protein kinase Cε fragment into the cells. The intracellular molar concentration of the introduced peptide was ≃10% of that applied outside. We found no significant effects of permeabilization on spontaneous, phorbol ester- modulated, or norepinephrine-modulated contraction rates. Similarly, the expression of c-fos mRNA (measured 30 minutes after permeabilization) and the incorporation of [¹⁴C]phenylalanine following agonist stimulation (measured 3 days after permeabilization) were not altered by saponin permeabilization. Finally, permeabilization of cells in the presence of a protein kinase C pseudosubstrate peptide, but not a control peptide, inhibited phorbol ester- induced [¹⁴C]phenylalanine incorporation into proteins by 80%. Our results demonstrate a methodology for the introduction of peptides into neonatal cardiac myocytes that allows study of their actions without substantial compromises in cell integrity.