Journal of Clinical and Molecular Endocrinology

Letter to Editor

The well-known effect of the active form of vitamin D₃, 1,25(OH)₂ vitamin D₃ (1,25-D₃), on calcium metabolism, cell proliferation and differentiation is mediated by genomic and nongenomic action [1,2]. The wide 1,25-D₃ receptors distribution and the expression of 1α-hydroxylase in the male reproductive tract reinforces a pivotal role of this hormone for the active and complete spermatogenesis [3-5].

The Sertoli cell in the seminiferous tubules provides structural and nutritional support for the healthy development of germ cells [6]. The secretory functions of Sertoli cell depend on the activation of ionic channels which are regulated by 1,25-D₃ rapid responses to induce exocytosis of a fluid rich in ions, proteins and growth factors critical for male fertility [7,8]. Studies carried out by our group over the last years have revealed important aspects regarding the effects of 1,25-D₃ stimulation of calcium influx by different ionic channels and signal transduction pathways, including cross talk by second messengers modulating the channel activities [9].

The electrophysiological properties of Sertoli cells indicate that the precise control of the electrochemical gradient is involved in the maintenance of the secretory process [7,9]. The addition of high K⁺ in the extracellular media caused a strong depolarization of Sertoli cells followed by repolarization with the efflux of potassium ions through the voltage-gated K⁺ channels. In the presence of 1,25-D₃, the efflux of K⁺ ions was recorded after 10 minutes of incubation and it was blocked by TEA, indicating a secretory activity of Sertoli cell through the Ca²⁺ conventional secretory pathway.

Our new data shows the stimulatory effect of 1,25-D₃ on whole-cell K⁺ currents inhibited by tetraethylammonium, TEA, a broad-spectrum blocker of potassium channels indicating a repolarization of the Sertoli cell after stimulus. Stimulussecretion coupling in Sertoli cells involves multiple ionic channels that regulate the plasma membrane potential, intracellular calcium and secretion. Repolarization of the membrane potential is mediated by several K+-selective ionic channel proteins such as ATP sensitive potassium channel (KATP), voltage-gated channels (Kv), and Ca²⁺-activated K⁺ channels (KCa).

In summary, our results demonstrate for the first time that nongenomic 1,25-D₃ potentiation of potassium currents couple to exocytosis in primary culture of Sertoli cells. This effect appears to involve Ca²⁺ influx leading to K⁺ efflux and repolarization. We conclude that the steroid hormone 1,25-D₃ appears to play a functional role in male fertility via stimulation of Sertoli cell secretory activities in the testis.

References

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