PROPOFOL DOES NOT INHIBIT CALCIUM-INDUCED RELEASE OF BETA-ENDORPHIN FROM PERMEABILIZED MOUSE PITUITARY CELLS

Abstract

S528 INTRODUCTION: Propofol inhibits secretion of beta-endorphin from AtT-20 cells, a mouse pituitary cell line [1]. Cells were permeabilized with digitonin to investigate the biochemical basis of propofol's effects. The calcium concentration in permeabilized cells was fixed at 0 or 10 [micro sign]M, to determine whether propofol acts before or after the rise in calcium associated with secretion of neuropeptides. METHODS: Subconfluent AtT-20 cells grown in 12-well plates (4 wells per condition) were incubated at 37[degree sign]C for 60 minutes in 145 mM NaCl/15 mM HEPES pH 7.4/5.6 mM glucose/5.6 mM KCl/2.2 mM CaCl2,/0.5 mM MgCl2/0.5 mM sodium ascorbate. The cells were then incubated at 37[degree sign]C for 60 minutes in 139 mM potassium glutamate/20 mM PIPES pH 6.6/5 mM EGTA/5 mM MgCl2/5 mM ATP/0.5 mM sodium ascorbate (negative control). Experimental manipulations included addition of CaCl2 to a free concentration of 10 [micro sign]M, 2 [micro sign]M digitonin, and propofol (0 to 100 [micro sign]M). The supernatants were analyzed for beta-endorphin release by ELISA. RESULTS: Raising extracellular calcium to 10 [micro sign]M did not induce secretion from nonpermeabilized cells. beta-endorphin was released from digitonin-permeabilized cells in a calcium-dependent fashion. Propofol (0-100 [micro sign]M) did not inhibit release of beta-endorphin from permeabilized cells. (Figure 1)Figure 1DISCUSSION: Propofol did not inhibit calcium-induced release of beta-endorphin from permeabilized cells, but propofol does inhibit stimulated secretion of beta-endorphin from intact cells. Thus, propofol does not inhibit secretory steps subsequent to the rise in calcium. Instead, propofol inhibits a process required for secretion that occurs at or prior to the rise in calcium. One possible site of action would be entry of calcium into cells via calcium channels.