The response of human spermatozoa to chemoattractants

The effect of the chemoattractant bourgeonal on [Ca\(^{2+}\)]i and chemotaxis in human sperm was investigated. Burgeonal induced a dose-dependent, slowly-developing tonic elevation in [Ca\(^{2+}\)]i, The response was dependent on capacitation. In low-Ca\(^{2+}\) or EGTA-buffered saline the response to bourgeonal was inhibited. Pretreating spermatozoa with bis-phenol (20μM) to release stored Ca\(^{2+}\) did not alter the response. Thus bourgeonal acts primarily by inducing Ca\(^{2+}\) influx. Treatment of sperm with bourgeonal caused an increase in [cAMP]. When cells were pretreted with bourgeonal in low-Ca\(^{2+}\)saline, subsequent introduction of Ca\(^{2+}\) resulted in a single, large [Ca\(^{2+}\)]i transient in >75% of the cells, indicating that sudden influx of Ca\(^{2+}\) caused closure of the bourgeonal-sensitive Ca\(^{2+}\)- channel. This negative feedback was not modulated by IBMX (1mM) or dbcAMP (1mM), indicating that cAMP was not involved and that a direct action Ca\(^{2+}\) was more likely. Both Ni\(^{2+}\) (10μM) and La\(^{3+}\) (100μM) inhibited the action of bourgeonal on [Ca\(^{2+}\)]i, suggesting a possible role of CNG channels. Exposing sperm to a temporal bourgeonal gradient caused a series of transient [Ca\(^{2+}\)]i elevations in >20% of the cells. A gradient of progesterone (another characterised chemoattractant for human sperm) induced similar Ca\(^{2+}\) oscillations (in >20% of the cells), which increased in amplitude and frequency in response to the increasing progesterone concentration. Human spermatozoa responded chemotactically to a 1nM bourgeonal gradient, Chemotaxis was dependent on capacitation. The response was inhibited in low [Ca\(^{2+}\)]o but was unaltered by TMB-8 (an inhibitor of stored Ca\(^{2+}\) store release), thus showing a dependence on Ca\(^{2+}\) influx similar to the [Ca\(^{2+}\)]i signal