Density distribution of guinea pig myenteric plexus nerve endings containing immunoreactive substance P

The present study was performed to investigate how myenteric plexus nerve endings containing substance P are distributed in sucrose density gradients in relation to nerve endings capable of taking up 3H-acetylcholine or 14C-noradrenaline. The peak of substance P-immunoreactivity (ISP) was found at a density of 1.157 +/- 0.001 g X ml-1, that of 3H-radioactivity at 1.160 +/- 0.002 and that of 14C-radioactivity at 1.162 +/- 0.002 g X ml-1 (mean +/- SEM, N = 6); there was considerable overlap. In a second set of experiments, the resuspended P2-pellet was layered upon a discontinuous density gradient consisting of 0.6, 1.0, 1.2 and 1.4 M sucrose. Nine fractions were recovered. There was a 2.5-3.4-fold increase in the relative specific activity of ISP in the 1.2 M fraction (density = 1.154 g X ml-1) and the adjoining interfaces. Conventional electron microscopy showed that synaptosomal elements were present in the transmitter-enriched fractions. It is concluded that the substance P-containing nerve endings of the guinea pig myenteric plexus co-distribute (and may be co-purified with) nerve endings utilizing noradrenaline or acetylcholine on sucrose density gradients.