Hemolysate-Mediated Renal Vasoconstriction and Hypersensitization

Abstract

The present studies measured vessel diameter, before and after addition of hemolysate, in isolated afferent arterioles (AA) and efferent arterioles (EA) obtained from the rat kidney. Human red blood cells (RBC) were hemolyzed in distilled water and membranes were discarded after centrifugation. Hemolysate added to the bath solution caused vigorous AA and E4 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 contraction nor the hypersensitization were mimicked by pure human hemoglobin. The vasoconstrictive responses in the AA and EA were accompanied by increased cytosolic-free calcium concentration. Further purification (desalting) of the hemolysate to remove substances of ≤ 1000 Da (which include ATP) did not eliminate the vasoconstrictive component from the hemolysate. Finally, cultured rat aortic vascular smooth muscle cells also demonstrated a rapid increase in (Ca²⁺i) when exposed to hemolysate. This increase in (Ca²⁺i) was, in part, dependent on Ca²⁺ influx since it could be attenuated with diltiazem (10⁻⁵M). In conclusion, hemolysate contains a factor which induces contractions of the isolated rat kidney AA and EA arid rapid elevations in (Cd²⁺i). This factor, from hemolyzed RBC, is not hemoglobin itself.

Key Words:

• Kidney
• Afferent arteriole
• Efferent arteriole
• VSMC
• Renal vascular resistance
• Fluorescence
• Fura-2