1. Department of Physiology and Biophysics, Albert Einstein College of Medicine, 1300 Morris Park Avenue, Bronx, New York 10461, Danish Centre for Respiratory Adaptation, Department of Zoophysiology, Institute of Biological Sciences, University of Aarhus, DK-8000 Aarhus C, Denmark, Department of Biochemistry, University of Antwerp, Universiteitsplein 1, B-2610 Antwerp, Belgium, and Department of Biology, Faculty of Science, Shizuoka University, 836 Oya, Shizuoka 422-8529, Japan