Different Localization of ATP Sensitive K+ Channel Subunits in Rat Testis

Physiological role of potassium channels in mammalian germ cell differentiation, maturation, and capacitation

BACKGROUND

Ion channels are essential for differentiation and maturation of germ cells, and even for fertilization in mammals. Different types of potassium channels have been identified, which are grouped into voltage-gated channels (Kv), ligand-gated channels (Kligand), inwardly rectifying channels (Kir), and tandem pore domain channels (K2P).

MATERIAL-METHODS

The present review includes recent findings on the role of potassium channels in sperm physiology of mammals.

RESULTS-DISCUSSION

While most studies conducted thus far have been focused on the physiological role of voltage- (Kv1, Kv3, and Kv7) and calcium-gated channels (SLO1 and SLO3) during sperm capacitation, especially in humans and rodents, little data about the types of potassium channels present in the plasma membrane of differentiating germ cells exist. In spite of this, recent evidence suggests that the content and regulation mechanisms of these channels vary throughout spermatogenesis. Potassium channels are also essential for the regulation of sperm cell volume during epididymal maturation and for preventing premature membrane hyperpolarization. It is important to highlight that the nature, biochemical properties, localization, and regulation mechanisms of potassium channels are species-specific. In effect, while SLO3 is the main potassium channel involved in the K+ current during sperm capacitation in rodents, different potassium channels are implicated in the K+ outflow and, thus, plasma membrane hyperpolarization during sperm capacitation in other mammalian species, such as humans and pigs.

CONCLUSIONS

Potassium conductance is essential for male fertility, not only during sperm capacitation but throughout the spermiogenesis and epididymal maturation.

The Role of Sperm Membrane Potential and Ion Channels in Regulating Sperm Function

During the last seventy years, studies on mammalian sperm cells have demonstrated the essential role of capacitation, hyperactivation and the acrosome reaction in the acquisition of fertilization ability. These studies revealed the important biochemical and physiological changes that sperm undergo in their travel throughout the female genital tract, including changes in membrane fluidity, the activation of soluble adenylate cyclase, increases in intracellular pH and Ca2+ and the development of motility. Sperm are highly polarized cells, with a resting membrane potential of about -40 mV, which must rapidly adapt to the ionic changes occurring through the sperm membrane. This review summarizes the current knowledge about the relationship between variations in the sperm potential membrane, including depolarization and hyperpolarization, and their correlation with changes in sperm motility and capacitation to further lead to the acrosome reaction, a calcium-dependent exocytosis process. We also review the functionality of different ion channels that are present in spermatozoa in order to understand their association with human infertility.

Carvacrol treatment opens Kir6.2 ATP-dependent potassium channels and prevents apoptosis on rat testis following ischemia-reperfusion injury model

Testicular torsion is a urological problem that causes subfertility and testicular damage in males. Testis torsion and detorsion lead to ischemia–reperfusion (IR) injury in the testis. Testicular IR injury causes the increase of reactive oxygen species (ROS), oxidative stress (OS) and germ cell-specific apoptosis. In this study, we aimed to investigate whether Carvacrol has a protective effect on testicular IR injury and its effects on Kir6.2 channels, which is a member of adenosine triphosphate (ATP)-dependent potassium channels. In the study, 2–4 months old 36 albino Wistar rats were used. For experimental testicular IR model, the left testis was rotated counterclockwise at 720° for two hours, and after two hours following torsion, detorsion was performed. Carvacrol was dissolved in 5% Dimethyl Sulfoxide (DMSO) at a dose of 73 mg/kg and half an hour before detorsion, 0.2 mL was administered intraperitoneally. In testicular tissues, caspase 3 and Kir6.2 immunoexpressions were examined. Serum malondialdehyde (MDA) and testosterone levels were measured. Apoptotic cells and serum MDA levels were significantly decreased and Kir6.2 activation was significantly increased in Carvacrol-administrated IR group. As a result of our study, Carvacrol may activates Kir6.2 channels and inhibits apoptosis and may have a protective effect on testicular IR injury.

Carbamazepine-induced sperm disorders can be associated with the altered expressions of testicular KCNJ11/miR-let-7a and spermatozoal CFTR/miR-27a

Male infertility is a global health problem, and the underlying molecular mechanisms are not clearly known. Ion channels and microRNAs (miRNAs), known to function in many vital functions in cells, have been shown to play a significant role in male infertility through changes in their expressions. The study aimed to evaluate the alterations of testicular and/or spermatozoal potassium voltage-gated channel subfamily J member 11 (KCNJ11), Cystic fibrosis transmembrane conductance regulator (CFTR), miR-let-7a and miR-27a expressions in carbamazepine-related male infertility. Here, we showed that carbamazepine reduced sperm motility, increased abnormal sperm morphology, and impaired hormonal balance as well as increased relative testis weight and decreased relative seminal vesicle weight. On the other hand, downregulated KCNJ11 and upregulated miR-let-7a expressions were determined in testis (p < .05). Also, downregulated KCNJ11 and upregulated CFTR and miR-27a expressions were found in spermatozoa (p < .05). Interestingly, altered testicular KCNJ11 and miR-let-7a expressions were correlated with decreased sperm motility and elevated sperm tail defect. Besides, spermatozoal CFTR and miR-27a expressions positively correlated with sperm tail defects. The results indicated a significant relationship between ion channel and/or miRNA expression alterations and impaired sperm parameters due to carbamazepine usage.

Verapamil-induced ion channel and miRNA expression changes in rat testis and/or spermatozoa may be associated with male infertility

The effect of verapamil, a calcium channel blocker, on male fertility in terms of ion channel and miRNA gene expressions in testis/spermatozoa was evaluated in this study. Rats were divided into sham and verapamil groups (n = 15). Verapamil was performed orally for 60 days. Sperm parameters and levels of serum follicle-stimulating hormone (FSH), luteinising hormone (LH) and testosterone (T) hormones were analysed. Alterations of microRNA (miRNA) and ion channel gene expressions in spermatozoa/testis were detected by using qPCR. Verapamil treatment reduced sperm concentration. Increased serum FSH, LH and T hormone levels were detected. Upregulated transient receptor potential cation channel subfamily V member 5 (TRPV5) and potassium voltage-gated channel subfamily J member 11 (KCNJ11) gene expressions and downregulated miR-let-7b, miR-10a, miR-320 and miR-760 expressions were found in testis of verapamil group. However, upregulated anoctamin 1 (ANO1), ATP-binding cassette subfamily C member 9 (ABCC9), miR-27a and miR-130a expressions and downregulated miR-20a, miR-92a, miR-132, miR-320 and miR-760 expressions were detected in spermatozoa. In addition, these altered gene expressions were found to be associated with decreased sperm concentration. The results indicate that the changes in testicular and/or spermatozoal ion channels and miRNA expressions due to verapamil treatment may affect male fertility.

Blocking of the ATP sensitive potassium channel ameliorates the ischaemia-reperfusion injury in the rat testis

There is increasing evidence that the effects of administered ATP sensitive potassium (KATP ) channel openers or blockers during ischaemia are still controversial in many organs/tissues. Testicular torsion detorsion which causes ischaemia-reperfusion (IR) injury, cannot be predicted, thus an effective drug should be administered during or after the ischaemia. The aim of this study was to examine whether the administration of KATP channel openers or blockers during ischaemia ameliorates IR injury in the testis. Eight-week-old male Sprague-Dawley rats were subjected to 2 h right testicular ischaemia followed by 24 h reperfusion. The selective mitochondrial (mito) KATP channel blocker, 5-hydroxydecanoate (5-HD) (40 mg/kg), the non-selective KATP channel blocker glibenclamide (5 mg/kg), the selective mito KATP channel opener diazoxide (10 mg/kg) and the non-selective KATP channel opener cromakalim (300 μg/kg) were administered intraperitoneally 15 min prior to the ischaemia or 75 min after the induction of ischaemia. Tissue damage was evaluated by malondialdehyde concentration, myeloperoxidase activity, histological evaluation and TdT-mediated dUTP nick end labelling assay in the testis. There was a significant increase in oxidative stress, neutrophil infiltration, histological damage and apoptosis in the testicular IR model. A significant reduction in the testicular IR injury was observed with the administration of glibenclamide, but not 5-HD, diazoxide or cromakalim during ischaemia. The administration of non-selective KATP channel blocker glibenclamide ameliorated the testicular IR injury. On the other hand, the selective mito KATP channel blocker, 5-HD and KATP channel openers did not reduce the testicular IR injury. These data suggest that blocking of the membrane KATP channel may have a protective effect during the testicular ischaemia. Glibenclamide could be an effective drug to manage the post-ischaemic injury caused by the testicular torsion-detorsion.

K+ and Cl- channels and transporters in sperm function

To succeed in fertilization, spermatozoa must decode environmental cues which require a set of ion channels. Recent findings have revealed that K(+) and Cl(-) channels participate in some of the main sperm functions. This work reviews the evidence indicating the involvement of K(+) and Cl(-) channels in motility, maturation, and the acrosome reaction, and the advancement in identifying their molecular identity and modes of regulation. Improving our insight on how these channels operate will strengthen our ability to surmount some infertility problems, improve animal breeding, preserve biodiversity, and develop selective and secure male contraceptives.

Localization of the ATP-sensitive K(+) channel regulatory subunits SUR2A and SUR2B in the rat brain

ATP-sensitive K(+) (K(ATP)) channel subunits SUR2A and SUR2B in the rat brain were investigated by RT-PCR assay, western blot analysis, in situ hybridization histochemistry, and immunohistochemical staining. The results show that the mRNA and protein of SUR2A and SUR2B are expressed in whole rat brain extracts and selected regions. SUR2 mRNA is widely expressed in many neurons and glial cells as revealed by in situ hybridization histochemistry. Immunohistochemical staining shows SUR2A to be widely expressed in neurons of the brain, especially in the large pyramidal neurons and their main dendrites in the neocortex and in the Purkinje cells of the cerebellar cortex. In contrast to SUR2A, SUR2B is potently expressed in small cells in the corpus callosum and cerebellar white matter, but is also weakly expressed in some neurons. Double immunostaining shows SUR2B to be localized in astrocytes and oligodendrocytes, while SUR2A is only localized in oligodendrocytes. These results suggest that SUR2A might be mainly a regulatory subunit of the K(ATP) channel in most neurons and part of oligodendrocytes, while SUR2B might be mainly a regulatory subunit of the K(ATP) channel in astrocytes, oligodendrocytes, and some neurons.