1. Department of Physiology and Biophysics, University of Puerto Rico, San Juan, PR 00936; Department of Physiology and Biophysics, University of Alabama in Birmingham, University Station, Birmingham, AL 35294, U.S.A.
2. Departments of Physiology and Biophysics, Medicine and Physics, University of Alabama in Birmingham, University Station, Birmingham, AL 35294, U.S.A.
3. Department of Biostatistics, University of Alabama in Birmingham, University Station, Birmingham, AL 35294, U.S.A.