Mobilisation of stored calcium in the neck region of human sperm - a mechanism for regulation of flagellar activity
Published: 1 July 2008
Kweku Bedu-Addo1, Sarah Costello2, Claire Harper3, Gisela Machado-Oliveira2, Linda Lefievre4, Christopher Ford4, Christopher Barratt5 and Stephen Publicover2,*
1Kwame Nkrumah University of Science and Technology, Kumasi, Ghana, 2School of Biosciences, University of Birmingham, UK 3School of Biological Sciences, University of Liverpool, UK, 4Department of Medicine, University of Birmingham, UK and 5Medical School, Ninewells Hospital, Dundee, UK
Calcium signalling plays a pivotal role in sperm physiology, being intimately involved in the regulation of acrosome reaction, chemotaxis and hyperactivation. Here we describe briefly the mechanisms of calcium regulation in somatic cells and the ways in which these mechanisms have been adapted to function in mature spermatozoa. We then consider recent data from this and other laboratories on the responses of sperm to three compounds: progesterone and nitric oxide (both products of the cumulus oophorus) and 4-aminopyridine. All of these compounds induce calcium signals in the posterior sperm head and neck region and, when applied at appropriate concentrations, modify flagellar activity, causing asymmetric bending of the proximal flagellum. We argue that these effects reflect a common mode of action, mobilisation of calcium stored in the sperm neck region. Finally we consider the nature of calcium signalling pathways in sperm. We suggest that this highly specialised and extremely polarised cell, though working with the same calcium signalling 'tools' as those of somatic cells, employs them to generate unusually 'hard-wired' calcium signals that do not act to integrate stimuli. 'Leakage' between these calcium signalling pathways will generate inappropriate responses, compromising functioning of the cell.