NP-induced biophysical and biochemical alterations of rat testicular Sertoli cell membranes related to disturbed intracellular Ca2+ homeostasis

Nonylphenol (NP) is a representative endocrine disruptor that has an adverse effect on male reproduction and posses direct hazard to Sertoli cells, but the mechanism remains incompletely elucidated. In the present study, based on the structural comparability and high affinity between NP and membrane phospholipid molecules, we tested the hypothesis that entrance of NP into Sertoli cells would alter membrane biophysical characteristics and biochemical functions. First, we used gas chromatography–mass spectrometry (GC–MS) to investigate the distribution and pharmacokinetics of NP in Sertoli cells with the result revealing that NP could penetrate plasma membrane of Sertoli cells. Meanwhile, Sertoli cells treated with NP exhibited abnormal membrane potential; that is an early depolarization following short treatment and hyperpolarization after longer treatment with the highest concentration of NP. Studies on the membrane dynamics indicated that the NP exposure rendered increased membrane fluidity and decreased microviscosity and molecular order. The result of lactate dehydrogenase (LDH) leakage assay demonstrated that NP increased membrane permeability in time–dose-dependent manners. Atomic force microscopic (AFM) imaging was applied to examine the membrane topography, and the images showed that NP treatment caused disturbance of membrane topography. The activities of plasma membrane Ca2+-ATPase, Ca2+–Mg2+-ATPase and Na+–K+-ATPase were also changed following NP exposure. However, FSH receptor as an important membrane protein was not significantly altered. All the above changes led to the disturbed intracellular Ca2+ homeostasis which was an important signal triggering apoptosis. Hence, cellular membranes represented a plausible target for NP-induced cytotoxicity.