Onion peel extract and its constituent, quercetin inhibits human Slo3 in a pH and calcium dependent manner

Abstract

Sperm function and male fertility are closely related to pH dependent K + current (KSper) in human sperm, which is most likely composed of Slo3 and its auxiliary subunit leucine-rich repeat-containing protein 52 (LRRC52). Onion peel extract (OPE) and its major active ingredient quercetin are widely used as fertility enhancers; however, the effect of OPE and quercetin on Slo3 has not been elucidated. The purpose of this study is to investigate the effect of quercetin on human Slo3 channels. Human Slo3 and LRRC52 were co-transfected into HEK293 cells and pharmacological properties were studied with the whole cell patch clamp technique. We successfully expressed and measured pH sensitive and calcium insensitive Slo3 currents in HEK293 cells. We found that OPE and its key ingredient quercetin inhibit Slo3 currents. Inhibition by quercetin is dose dependent and this degree of inhibition decreases with elevating internal alkalization and internal free calcium concentrations. Functional moieties in the quercetin polyphenolic ring govern the degree of inhibition of Slo3 by quercetin, and the composition of such functional moieties are sensitive to the pH of the medium. These results suggest that quercetin inhibits Slo3 in a pH and calcium dependent manner. Therefore, we surmise that quercetin induced depolarization in spermatozoa may enhance the voltage gated proton channel (Hv1), and activate non-selective cation channels of sperm (CatSper) dependent calcium influx to trigger sperm capacitation and acrosome reaction.

Iberiotoxin and clofilium regulate hyperactivation, acrosome reaction, and ion homeostasis synergistically during human sperm capacitation

“…One opinion considers that SLO3 is the main potassium channel in human sperm. (Wijerathne et al, 2017(Wijerathne et al, , 2019. Therefore, we think that IbTX acts on the SLO1 potassium channel when human sperm are treated with this inhibitor.…”

“…IbTX is considered a SLO1 specific inhibitor with the IC50 at about 2–10 nM (Yu et al, 2016). Wijerathne et al heterologously expressed hSlo3 and hLRRC52 in HEK293 cells and found that 100 nM IbTX does not affect the I hSLO3 (Wijerathne et al, 2017, 2019). Therefore, we think that IbTX acts on the SLO1 potassium channel when human sperm are treated with this inhibitor.…”

In vitro assessment of Prunus japonica seed extract on human spermatozoa hypermotility and intracellular alkalization

“…Traditional medicine has been extensively used to ameliorate men's health problems in Korea (Jiang et al, 2017). In particular, ion channel‐targeted herbal medicines and their mechanisms of action in sperm for treating male infertility are being researched (Chae et al, 2017; Wijerathne et al, 2019). Our study demonstrated the positive action of PJE on sperm motility via the sperm hHv1 proton channel.…”

Research progress on ion channels and their molecular regulatory mechanisms in the human sperm flagellum

“…Among them, KSper plays a principal role in mouse sperm but is not clear in human sperm 37,92 . It can hyperpolarize the membrane potential from about −40 mV in the resting state to about −60 mV after being activated under alkaline conditions, 37,94,95 which decreases the electrochemical driving force of Ca 2+ to influx through CatSper channels 40,96 . If KSper is antagonized by inhibitors, the sperm will not show capacitation‐dependent hyperpolarization of the cell membrane 97 .…”