Membrane toxicity of the protein kinase C inhibitor calphostin A by a free-radical mechanism.

Abstract

The effects of calphostin A on cytoplasmic calcium levels, receptor-mediated calcium release, and membrane input resistance were measured in neuroblastoma cells. Calphostin A is a lipophilic, light-sensitive perylenequinone that generates singlet oxygen when illuminated. It inhibits the activity of protein kinase C (IC50 = 250 nM), but only in the presence of light. Phorbol esters normally attenuate carbachol-evoked calcium release. This effect was blocked by simultaneous exposure to light and calphostin A (40 nM) for 30 min. At higher doses (0.5-1 microM) calphostin A also approximately doubled the resting calcium level and decreased cell input resistance by 51%. These toxic effects did not occur in the dark or after preincubation with the antioxidant alpha-tocopherol. These data support the hypothesis that the calphostins act by partitioning into the membrane and producing singlet oxygen and endoperoxides which then irreversibly modify protein kinase C and other membrane proteins and lipids.

• Authors: S S Wang, C Mathes, S H Thompson
• Journal: Neuroscience letters (Neurosci Lett) Vol. 156 Issue 1-2 Pg. 145-8 (Jun 25 1993) ISSN: 0304-3940 [Print] Ireland
• PMID: 7692361 (Publication Type: Journal Article, Research Support, U.S. Gov't, P.H.S.)

Chemical References

• Fluorescent Dyes
• Free Radicals
• Naphthalenes
• Polycyclic Compounds
• fura-2-am
• calphostin A
• Carbachol
• Protein Kinase C
• Calcium
• Fura-2

Topics

• Animals
• Calcium (metabolism)
• Carbachol (pharmacology)
• Cell Line
• Cell Membrane (drug effects, physiology)
• Fluorescent Dyes
• Free Radicals (metabolism)
• Fura-2 (analogs & derivatives)
• Homeostasis
• Kinetics
• Naphthalenes
• Neuroblastoma
• Polycyclic Compounds (toxicity)
• Protein Kinase C (antagonists & inhibitors)
• Tumor Cells, Cultured