PROPOFOL INDUCES CHANGES IN THE CYTOSOLIC-FREE CALCIUM-CONCENTRATION AND THE CYTOSKELETAL ORGANIZATION OF CULTURED HUMAN GLIAL-CELLS AND PRIMARY EMBRYONIC RAT-BRAIN CELLS

Background: The site of action of the intravenous anesthetic drug propofol is uncertain. Therefore, we examined the effects of propofol on the cytosolic free calcium levels of cultured primary embryonic rat brain cells (80-85% neurons), and on the organization of the cytoskeleton in these rat cells and in a model system of cultured human glial cells (astrocytes). Methods: Propofol was added to the cells as the clinically available solution Diprivan. Cytosolic free calcium changes in neurons were studied using Fura2 and a single-cell microfluorometric method. Fluorescence microscopy was used to study the organization of actin filaments and tubulin in detergent-extracted cells. Results: An increase in the cytosolic free calcium concentration of 116 +/- 39 nM was seen shortly after the addition of 0.3 mu g.ml(-1) propofol, and a propofol concentration of 0.03 mu g.ml(-1) resulted in an increase in cytosolic free calcium concentration of the same magnitude, 119 +/- 42 nM. Most of the calcium (60-75%) came from the extracellular environment, and the rest was from intracellular stores. When neurons were depleted of intracellular calcium by 1,2-bis-5-methyl-amino-phenoxylethane-N,N'-tetra-acetoxymethylacetate (MAPT/AM), no changes were seen in the actin organization of the cytoskeleton. Actin organization was affected by all concentrationsof propofol, 0.3-50 mu g.ml(-1) (1.7-280 mu M), when exposure to the drug was achieved by a 30-min incubation. After the incubation, the exposed cells mere more rounded and exhibited increased ruffling activity, both at the periphery and on the cellular surface, and ring-shaped actin structures were also seen. These effects were concentration dependent and reversible, and reached a maximum after 20 min of incubation. Propofol had no apparent effect on the organization of tubulin. Conclusions: Propofol induced changes in the cytoskeletal organization of actin in cultured rat neurons and human glial cells. These changes must have been due to the increase in intracellular calcium seen shortly after the addition of propofol, since no effects on actin organization were seen when intracellular calcium was depleted.