[1] Univ London Imperial Coll Sci Technol & Med, Inst Reprod & Dev Biol, London W12 0NN, England
[2] Univ Turku, Dept Physiol, FIN-20520 Turku, Finland
[3] Consejo Nacl Invest Cient & Tecn, Inst Biol & Med Expt, RA-1428 Buenos Aires, DF, Argentina
[4] Univ Helsinki, Biomedicum, Dept Physiol, FIN-00014 Helsinki, Finland