Picture created by @embryostories
Rapid ‘switching’ of human sperm motility
Motility of human sperm is typically quantified as a ‘snapshot’, estimating the proportion of cells showing each motility type. However, observation of cells for several seconds suggests that behaviour of individual sperm can change rapidly (2). Such behavioural switching may be adaptive, for instance during ascent of the female tract by ‘hopping’. We captured behaviour of individual sperm over a period of 180 s (9000 frames at 50 Hz), using a motorized stage to centre the cell in the field of view when required.
For analysis 4 behaviours were defined. Types 1-3 resembled activated, transitional and hyperactivated behaviours. Type 3 cells occasionally arrested with the anterior flagellum in a ‘J’ shape (type 4). Each of 180, 1 s periods were assigned to one of these behaviours. A subset of cells was also analysed using Metamorph software to generate continuous 3 minute tracks. Fractal dimension analysis (1) confirmed that visual analysis reliably identified types and changes of behaviour. % hyperactivation under each incubation condition was separately assessed by CASA.
In control recordings (EBSS pH 7.4) 16/18 cells showed repeated, abrupt transitions in behaviour (mean=6.4±0.8 min-1, n=18). Under conditions that raise [Ca2+]i and stimulate hyperactivated motility (2 mM 4-aminopyridine at pH8.5, hyperactivation increased from 4±2% to 35±4 %), switching between behaviours persisted (9/20 cells switched within 180 s) but the duration of periods of type 3/ 4 (hyperactivated-like) behaviour from 5.9±0.5 seconds (control) to 82.3±11.2 seconds (P<5*10-8). Duration of type 1 (activated-like) behaviour was little affected (12.9±1.7 and 8.8±2.7 seconds respectively; P=0.2). We conclude that behavioural switching occurs continuously and that stimuli that induce hyperactivation greatly prolong periods of hyperactivated behaviour.
1.Mortimer (1998) Reprod Fertil Dev. 10:465-9. 2.Pacey et al (1997) Hum Reprod Update 3:185–93.