STATISTICAL EVIDENCE FOR 2 MAJOR PROTEINS IN FREEZE-FRACTURED GASTRICPARIETAL-CELL TUBULOVESICLES AND CANALICULUS

In a previous work, resting and acid-secreting rabbit gastric mucosa w ere freeze-fractured and shadowed at 45 degrees with Pt-C. The shadow widths of proteic particles of tubulovesicle and canaliculus membranes were measured and compared. It was concluded that the frequency distr ibutions of widths are significantly different in resting and secretin g membranes and that each distribution accounts for several subpopulat ions of homogenous particles. In the present study, an attempt is made to describe the experimental distributions as a mixture of those of t wo major proteins, say A and B and their aggregates (P;A, AB and BB). The modelling, although simple, gave a very satisfactory statistical f it between observed and computed distributions. The comparison of para meters calculated from histamine and ranitidine experimental data furt her improves the fits and finally, component A accounts for 69% of the particles. Most replica of A particles are heart-shaped and the media n shadow widths are 6.1 and 6.8 nm in canaliculus and tubulovesicles r espectively. The component B accounts for 31% of the particles. They m ainly appear as small barrels and the median shadow widths are 8.8 and 10.3 nm in canaliculus and tubulovesiles respectively. According to c alculated parameters and observed particle replica, the onset of secre tion does not change the relative ratio of proteins but changes their shapes. Component A should be the (H+,K+)ATPase whereas debate on the identity of B is wide open.