Possible Involvement of Calmodulin in the Maintenance of Plasma Membrane Integrity in Oat Protoplasts both under Isotonic Conditions and after Hypotonic Shock

Abstract

Summary Protoplasts from Avena sativa were incubated with several calmodulin inhibitors including chlorpromazine (CPZ), trifluoperazine (TFP), tetracaine and R24571, and the effect on plasma membrane stability investigated under isotonic conditions as well as after hypotonic shock. Isotonic lysis was obtained if the drug concentration exceded 5 µM for R24571, 50 µM for TFP, 100 µM for CPZ and 400 µM for tetracaine, respectively. At lower drug concentrations protoplasts were stable in isotonic solution but the amount of lysis after hypotonic shock was strongly enhanced. Using tetracaine, lysis was additionally dependent on the external p H. The results suggest that calmodulin is important for maintaining plasma membrane integrity both under isotonic conditions and after osmotic shock.