Effect of cryoprotectant concentration on bovine oocyte permeability and comparison of two membrane permeability modelling approaches

Tania García-Martínez,Adam Z Higgins,Iris Martínez-Rodero,Ramila E Gulieva,Teresa Mogas,Steven F Mullen

doi:10.1038/s41598-021-94884-0

Abstract

The plasma membrane permeability to water and cryoprotectant (CPA) significantly impacts vitrification efficiency of bovine oocytes. Our study was designed to determine the concentration-dependent permeability characteristics for immature (GV) and mature (MII) bovine oocytes in the presence of ethylene glycol (EG) and dimethyl sulphoxide (Me2SO), and to compare two different modeling approaches: the two parameter (2P) model and a nondilute transport model. Membrane permeability parameters were determined by consecutively exposing oocytes to increasing concentrations of Me2SO or EG. Higher water permeability was observed for MII oocytes than GV oocytes in the presence of both Me2SO and EG, and in all cases the water permeability was observed to decrease as CPA concentration increased. At high CPA concentrations, the CPA permeability was similar for Me2SO and EG, for both MII and GV oocytes, but at low concentrations the EG permeability of GV oocytes was substantially higher. Predictions of cell volume changes during CPA addition and removal indicate that accounting for the concentration dependence of permeability only has a modest effect, but there were substantial differences between the 2P model and the nondilute model during CPA removal, which may have implications for design of improved methods for bovine oocyte vitrification.

Highlights

The plasma membrane permeability to water and cryoprotectant (CPA) significantly impacts vitrification efficiency of bovine oocytes
The CPA permeability was similar for Me2SO and ethylene glycol (EG), for both MII and GV oocytes, with the exception of the EG permeability for GV oocytes, which was substantially higher at low EG concentrations
Our results show nearly identical tendencies with both mathematical models: the water permeability decreases as EG or M e2SO concentration increases in both GV and MII oocytes, and the EG permeability decreases as EG concentration increases in GV oocytes

Summary

Introduction

The plasma membrane permeability to water and cryoprotectant (CPA) significantly impacts vitrification efficiency of bovine oocytes. Predictions of cell volume changes during CPA addition and removal indicate that accounting for the concentration dependence of permeability only has a modest effect, but there were substantial differences between the 2P model and the nondilute model during CPA removal, which may have implications for design of improved methods for bovine oocyte vitrification. The reason for oocytes susceptibility to low temperatures is due to their sensitivity at different cellular levels, such as the zona pellucida, plasma membrane, meiotic spindles and cytoskeleton (see r eview[4]) These subcellular structures change during maturation, which means that the developmental stage of the oocyte affects its cryobiological properties[5]. It has been shown that the permeability of the erythrocyte cell membrane to water and CPA is dependent on c oncentration[25], contrary to what previous studies have a ssumed[26]

Methods

Results

Discussion

Conclusion