Depolarization of sperm membrane potential is a common feature of men with subfertility and is associated with low fertilization rate at IVF

Abstract

STUDY QUESTIONAre significant abnormalities in outward (K+) conductance and resting membrane potential (Vm) present in the spermatozoa of patients undertaking IVF and ICSI and if so, what is their functional effect on fertilization success?SUMMARY ANSWERNegligible outward conductance (≈5% of patients) or an enhanced inward conductance (≈4% of patients), both of which caused depolarization of Vm, were associated with a low rate of fertilization following IVF.WHAT IS KNOWN ALREADYSperm-specific potassium channel knockout mice are infertile with defects in sperm function, suggesting that these channels are essential for fertility. These observations suggest that malfunction of K+ channels in human spermatozoa might contribute significantly to the occurrence of subfertility in men. However, remarkably little is known of the nature of K+ channels in human spermatozoa or the incidence and functional consequences of K+ channel defects.STUDY DESIGN, SIZE AND DURATIONSpermatozoa were obtained from healthy volunteer research donors and subfertile IVF and ICSI patients attending a hospital assisted reproductive techniques clinic between May 2013 and December 2015. In total, 40 IVF patients, 41 ICSI patients and 26 normozoospermic donors took part in the study.PARTICIPANTS/MATERIALS, SETTING, METHODSSamples were examined using electrophysiology (whole-cell patch clamping). Where abnormal electrophysiological characteristics were identified, spermatozoa were further examined for Ca2+ influx induced by progesterone and penetration into viscous media if sufficient sample was available. Full exome sequencing was performed to specifically evaluate potassium calcium-activated channel subfamily M α 1 (KCNMA1), potassium calcium-activated channel subfamily U member 1 (KCNU1) and leucine-rich repeat containing 52 (LRRC52) genes and others associated with K+ signalling. In IVF patients, comparison with fertilization rates was done to assess the functional significance of the electrophysiological abnormalities.MAIN RESULTS AND THE ROLE OF CHANCEPatch clamp electrophysiology was used to assess outward (K+) conductance and resting membrane potential (Vm) and signalling/motility assays were used to assess functional characteristics of sperm from IVF and ICSI patient samples. The mean Vm and outward membrane conductance in sperm from IVF and ICSI patients were not significantly different from those of control (donor) sperm prepared under the same conditions, but variation between individuals was significantly greater (P< 0.02) with a large number of outliers (>25%). In particular, in ≈10% of patients (7/81), we observed either a negligible outward conductance (4 patients) or an enhanced inward current (3 patients), both of which caused depolarization of Vm. Analysis of clinical data from the IVF patients showed significant association of depolarized Vm (≥0 mV) with low fertilization rate (P= 0.012). Spermatozoa with electrophysiological abnormities (conductance and Vm) responded normally to progesterone with elevation of [Ca2+]i and penetr...

Membrane Potential Assessment by Fluorimetry as a Predictor Tool of Human Sperm Fertilizing Capacity

“…In approximately 10% of the samples from infertile patients there was either a negligible outward conductance or an enhanced inward current, both of which caused Em depolarization. Analysis of clinical data from IVF patients showed a significant association of depolarized Em assessed by patch-clamp with low fertilization rate (Brown et al, 2016). These results point toward the correlation of the Em value of a sperm sample with its fertilizing capacity.…”

“…With this in mind, we aimed to analyze whether Em hyperpolarization relates to human sperm fertilizing capacity. It has been recently proposed that a certain degree of Em shift is associated with normal sperm function, as assessed by electrophysiology and IVF outcome (Brown et al, 2016). However, this study involved laborious techniques that hampered the analysis of many cells per patient.…”

“…Thus, it could be hypothesized that malfunction of K + channels in human sperm might also contribute to the occurrence of subfertility in men. Brown et al (2016) used whole-cell patch-clamp electrophysiology to assess the biophysical characteristics of sperm from men undergoing fertility treatments and compared to those from fertile, healthy donors. In approximately 10% of the samples from infertile patients there was either a negligible outward conductance or an enhanced inward current, both of which caused Em depolarization.…”

CFTR/ENaC-dependent regulation of membrane potential during human sperm capacitation is initiated by bicarbonate uptake through NBC

“…No ENaC current has been shown in electrophysiological examination of ejaculated cells so far. However, it is worth mentioning that in a recent study where 81 subfertile patients undergoing IVF/ICSI were investigated, one patient that presented depolarized Em associated with low IVF showed a large inward leak conductance (probably Na + ) (19). Unfortunately, this patient did not give permission for genetic analysis.…”

“…The regulation of membrane potential (Em) is an important event for fertility (18,19). Brown and coworkers showed that depolarized sperm Em values correlate with a higher percentage of IVF failure (19).…”