1. L. G. Navar, J. D. Imig, and K. D. Mitchell are in the Dept. of Physiology, Tulane University School of Medicine, New Orleans, LA 70112, USA; L. Zou was a Postdoctoral Fellow in that Department. A. Von Thun is in the Dept. of Internal Medicine of the Naval Medical Center, San Diego, CA, USA. C. T. Wang is in the Dept. of Internal Medicine, Section of Nephrology, General Hospital, Taipei, Taiwan.