Activators of protein kinase C and phenylephrine depolarize the astrocyte membrane by reducing the K+ permeability.

The membrane potential of astrocytes has been measured by monitoring the absorbance of a cyanine dye DiS-C2-(5). Ba2+, the phorbol ester 12-tetradecanoylphorbol myristateacetate (TPA) and the diglyceride, dioctanoylglycerol (DiC8) depolarize the membrane. Valinomycin which makes the membrane potential dependent on the K+ electrochemical potential evokes a hyperpolarization when added subsequently. The alpha-adrenergic receptor agonist phenylephrine was blocked by Ba2+, TPA, DiC8 and valinomycin. The results suggest that a protein kinase C-mediated reduction in the K+ permeability is responsible for the depolarizing effect of TPA, DiC8 and phenylephrine.