Electron paramagnetic resonance spectroscopy for the investigation of the fluidity of human spermatozoa plasma membranes: a feasibility study

Spermatozoal membrane perturbations may play a role in abnormal sperm funct ions. The objective of this investigation was to study the feasibility of m easuring membrane fluidity of isolated human sperm by electron paramagnetic resonance (EPR) spectroscopy and to compare the order parameter of spectra obtained from the sperm plasma membranes of living sperm of fertile men wi th that of infertile men. Ejaculates of infertile and fertile men were wash ed and the spermatozoa labelled with 5-doxylstearic acid (5-DSA) and 16-dox ylstearic-acid (16-DSA) (10 nmol per 4 x 10(7) sperm). The reporter group o f 5-DSA partitions into the outer, hydrophilic part of the sperm plasma mem brane, whereas that of 16-DSA is distributed in the inner hydrophobic part. The following results were obtained: (i) the lowest measurable cell count was 3.6 to 7 x 10(6) sperm and the interassay variance of the orderparamete r s was < 1%; (ii) swim-up experiments revealed a higher fluidity of sperm with a higher percentage of motility; (iii) sperm membranes of infertile pa tients exhibited a decreased fluidity of their plasma membranes in the pola r interface region of 5-DSA compared with volunteer semen donors and fertil e men (P = 0.002). No difference of membrane fluidity was found between the different groups using 16-DSA. It is concluded that EPR spectroscopy can b e used to study the fluidity of sperm plasma membranes in fertile and infer tile men.