Cellular and segmental distribution of Ca²⁺-pump epitopes in rat intestine

We used a monoclonal antibody (5F10) specific for the human erythrocyte plasma membrane Ca⁺⁺-pump to demonstrate the presence and distribution of Ca⁺⁺-pump epitopes in rat intestine. In paraffin embedded tissue sections, antibody 5F10 binds to epitopes in the basolateral membranes of absorptive cells in rat duodenum and portions of jejunum but not ileum. Western blot analysis of intestinal mucosal proteins with antibody 5F10 shows binding of antibody to major bands of Mr ≈ 135,000 and Mr ≈ 72,000, and to lesser bands of Mr ≈ 125,000 and Mr ≈ 27,000. This pattern was seen in mucosal homogenates of rat duodenal and jejunal cells and to a lesser extent in ileal cells. The Mr ≈ 135,000 band corresponds to the molecular weight of Ca⁺⁺-pumps in other tissues. The other bands correspond in size to known proteolytic fragments of the Ca⁺⁺-pump. Slot-blot analysis of nitrocellulose immobilized mucosal homogenates shows binding of 5F10 to be greatest in duodenum and least in ileum. Ca⁺⁺- transport studies by the everted gut sac technique show a correlation between vitamin D induction of active Ca⁺⁺-transport and the segmental distribution of Ca⁺⁺-pump epitopes.