SUBSTANCE-P AND EPIBATIDINE-EVOKED CATECHOLAMINE RELEASE FROM FRACTIONATED CHROMAFFIN CELLS

Bovine chromaffin cells were separated by density gradient centrifugat ion into subfractions enriched with either > 90% adrenaline- or 70-80% noradrenaline-producing cells. Concentrations of epibatidine (an alka loid with nicotinic receptor activity) as low as 10 nM released adrena line and noradrenaline from both fractions of cells maintained as mono layer cultures. The maximal effect was evoked by 30 nM epibatidine and was comparable to that evoked by 10 mu M nicotine. The catecholamine release from the noradrenaline fraction was 30-40% higher than from th e adrenaline fraction. Initial exposure to 50 nM epibatidine reduced r elease induced by a second exposure to the drug. There was cross-desen sitization between epibatidine and nicotine. Substance P inhibited the epibatidine-evoked catecholamine release from both fractions by up to 85% (IC50 = 3-5 mu M). The release of noradrenaline was inhibited mor e than that of adrenaline. In addition, substance P protected the chro maffin cells against desensitization of the nicotinic receptor by epib atidine. The C-terminal heptapeptide sequence of substance P was 10 x less active, two N-terminal sequences did not modulate the catecholami ne release.