1. Department of Physiology and Pharmacology, University of Strathclyde, Royal College, 204 George Street, Glasgow G1 1XW, U.K.
2. Department of Molecular Biology Laboratory, University of Strathclyde, Royal College, 204 George Street, Glasgow G1 1XW, U.K.
3. Department of Veterinary Clinical Studies, Royal School of Veterinary Studies, University of Edinburgh, Veterinary Field Station, Easter Bush, Roslin, Midlothian EH25 9RG, U.K.
4. Division of Biochemistry and Molecular Biology, Institute of Biomedical and Life Sciences, University of Glasgow, University Avenue, Glasgow G12 8QQ, U.K.