Abstract
We have successfully monitored the effect of progesterone and Ca2+ on artificially induced sperm capacitation in a real-time, noninvasive and label-free manner using an ion-sensitive field-effect transistor (ISFET) sensor. The sperm activity can be electrically detected as a change in pH generated by sperm respiration based on the principle of the ISFET sensor. Upon adding mouse sperm to the gate of the ISFET sensor in the culture medium with progesterone, the pH decreases with an increasing concentration of progesterone from 1 to 40 μM. This is because progesterone induces Ca2+ influx into spermatozoa and triggers multiple Ca2+-dependent physiological responses, which subsequently activates sperm respiration. Moreover, this pH response of the ISFET sensor is not observed for a Ca2+-free medium even when progesterone is introduced, which means that Ca2+ influx is necessary for sperm activation that results in sperm capacitation. Thus, a platform based on the ISFET sensor system can provide a simple method of evaluating artificially induced sperm capacitation in the field of male infertility treatment.
Highlights
Sperm capacitation is necessary for successful fertilization following sperm hyperactivation, acrosome reaction and chemotaxis towards the egg [1,2,3,4,5]
Medium including both progesterone and Ca ionophore must have greatly enhanced Ca2+ influx into spermatozoa, which contributed to a change in the electrical signal that resulted from sperm respiration (Figure 4)
Ca2+ influx into spermatozoa based on progesterone stimulation should have induced sperm respiration, which contributed to the change in pH obtained by the sperm-cultured gate ion-sensitive field-effect transistor (ISFET) sensor
Summary
Sperm capacitation is necessary for successful fertilization following sperm hyperactivation, acrosome reaction and chemotaxis towards the egg [1,2,3,4,5]. These events are recognized as Ca2+ -dependent physiological responses. Methods for evaluating sperm behaviors, such as acrosome reaction and chemotaxis of spermatozoa, but optical setups are mostly expensive and the preparation of reagents is time-consuming. It would be highly beneficial to develop a non-optical and noninvasive method for the quantitative evaluation of sperm behaviors. Intracellular Ca2+ regulates various cellular functions, including mitochondrial metabolism [13,14] and sperm respiration may be available as an indicator of sperm capacitation
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