Hemolysate-mediated renal vasoconstriction and hypersensitization

The present studies measured vessel diameter, before and after addition of hemolysate, in isolated afferent arterioles (AA) and efferent arterioles (E A) obtained from the rat kidney. Human red blood cells (RBC) were hemolyzed in distilled water and membranes were discarded after centrifugation. Hemo lysate added to the bath solution caused vigorous AA and EA contraction and , after washout, hypersensitized the AA and EA to doses of angiotensin II ( AII) which would normally only elicit 50% contraction (EC50). Neither the c ontraction nor the hypersensitization were mimicked by pure human hemoglobi n. The vasoconstrictive responses in the AA and EA were accompanied by incr eased cytosotic-free calcium concentration. Further purification (desalting ) of the hemolysate to remove substances of less than or equal to 1000 Da ( which include, ATP) did not eliminate the vasoconstrictive component from t he hemolysate. Finally, cultured rat aortic vascular smooth muscle cells al so demonstrated a rapid increase in (Ca(2+)i) when exposed to hemolysate. T his increase in (Ca(2+)i) was, in part, dependent on Ca2+ influx since if c ould be attenuated with diltiazem (10(-5) M). In conclusion, hemolysate con tains a factor which induces contractions of the isolated rat kidney AA and EA and rapid elevations in (Ca(2+)i). This factor, from hemolyzed RBC, is not hemoglobin itself.