Calmodulin content and activity in normal and coeliac duodenum.

Calmodulin is an important modulator of intracellular calcium processes and may be implicated in the calcium malabsorption of coeliac disease. The calmodulin content in extracts of duodenal biopsy specimens from 48 normal control subjects and 28 patients with coeliac disease was determined. Radioimmunoassay was used to measure immunoreactive calmodulin while a cyclic adenosine 3',5'-monophosphate phosphodiesterase activity assay was used to measure biologically active calmodulin. Calmodulin values measured by both assays were similar for control and disease groups. Mean (SEM) immunoreactive calmodulin values were 1.68 (0.09) micrograms/mg protein for controls and 1.67 (0.15) and 1.45 (0.15) micrograms/mg protein for partial and total villous atrophy respectively. These values were not significantly different. Biologically active calmodulin values were 2.77 (0.21), 1.82 (0.34), and 3.24 (0.33) micrograms/mg protein for control, partial, and total villous atrophy subjects respectively. The biologically active calmodulin values in the partial villous atrophy group were significantly lower than in controls and total villous atrophy subjects. In the phosphodiesterase assay, the calmodulin antagonist trifluoperazine inhibited the activity stimulated by purified calmodulin and by the extracts to the same extent. These results show that calmodulin values are normal in coeliac disease and provide no evidence that changes in calmodulin account for the abnormal calcium absorption in these patients.