Vol. 157, No. 3, 1988 December 30, 1988 BIOCHEMICAL AND BIOPHYSICALRESEARCH COMMUNICATIONS Pages 867-874 CHARACTERIZATION OF THE CALPASTATIN DEFECT IN ERYTHROCYTES FROM PATIENTS WITH ESSENTIAL HYPERTENSION Pontremoli, S., Salamino, F., Sparatore, B., De Tullio, R., Pontremoli, R.*, and Melloni, E. Institute of Biological Chemistry, University of Genoa, Viale Benedetto XV/1, 16132 Genoa, Italy *ISMI, Section of Nephrology, University of Genoa, Viale Benedetto XV/6, 16132 Genoa, Italy Received November 8, 1988 In erythrocytes of patients with essential hypertension the level of cal- pastatin activity was found to be significantly lower than in red cells of nor- motensive subjects (i). We now demonstrate, by Western blot analysis, that the decreased inhibitory activity is due to a corresponding decrease in the amount of the inhibitor protein. This is also supported by the observation that calpa- statins isolated and purified from erythrocytes of normotensive and hyperten- sive patients, have identical specific activity. Data are presented indicating that the decreased level of calpastatin cannot be ascribed to an accelerated decay of the inhibitor during the erythrocyte life span. Taken together the previous and pre~ent results further emphasize that an umbalanced proteolytic system may represent one of the molecular mechanisms responsible for those mem- brane abnormalities underlying the development of essential hypertension and its clinical complications. ~ 1988AcademicPress, Inc. It is generally accepted that in humans with essential hypertension and in rats with spontaneous hypertension (2) the red cell membrane structure and fun- ctions are significantly altered. This conclusion is supported by experimental data indicating= a decreased intracellular Na + content and cell volume (3), an enhanced phosphorylation of the anion transport protein (4) and an altered transport of cations (5-7) possibly resulting in an intracellular increase of free Ca 2+ (8, 9). Furthermore we have demonstrated that in erythrocytes of pa- tients with essential hypertension and also of genetically hypertensive rats, the level of calpastatin activity is profoundly reduced in comparison to red cells of normotensive controls (1, i0, 11). Based on these observations, a de- fective regulation of calpain resulting from a decreased activity of its natu- 0006-291X/88 $1.50 Copyr~ht © 1988 by Academic Press, ~c. 867 All r~h~ of reproduction in any form reserved.