Rat Pituitary Cells

Octamethylcyclotetrasiloxane (D4) is a highly volatile cyclic siloxane used to produce silicone polymers. D4 has been shown to attenuate the LH surge in rats, resulting i... More

Octamethylcyclotetrasiloxane (D4) is a highly volatile cyclic siloxane used to produce silicone polymers. D4 has been shown to attenuate the LH surge in rats, resulting in reduced litter sizes. However, it has been hypothesized that these biological effects observed only at high dose levels of D4 may be because of changes in membrane microviscosity (fluidity) leading to a non-specific mode of action. Here, we set out to determine if D4 increases membrane microviscosity and link this to membrane domain function alterations. The studies reported here support the hypothesis that D4 affects ovulation via a concentration-dependent, physical-chemical mode of action that is not specific for any particular component of the neuro-endocrine system and is, therefore, not endocrine disruption but a non-specific effect. Furthermore, D4 also increases the membrane fluidity of the hypothalamic cell membrane in vitro. It is expected that a similar response would occur in vivo. This alteration in membrane fluidity decreases the release of GnRH and kisspeptin. GnRH and kisspeptin are necessary for the pre-ovulatory LH surge from the pituitary. In the absence of a GnRH and kisspeptin release, there is no signal to the pituitary for the driver of the LH surge. D4 can change membrane fluidity in vitro and likely in vivo and associated behaviors of membrane proteins/lipoproteins of various kinds via non-specific mechanisms. Less

The hyperpolarization-activated cation current (Ih) exhibits a slowly activating time course of the current (Ih) when the cell membrane is hyperpolarized for an extended ... More

The hyperpolarization-activated cation current (Ih) exhibits a slowly activating time course of the current (Ih) when the cell membrane is hyperpolarized for an extended duration. It is involved in generating electrical activity in various excitable cells. Numerous structurally distinct compounds or herbal drugs have the potential to impact both the magnitude and gating kinetics of this current. Brivaracetam, a chemical analog of levetiracetam known to be a ligand for synaptic vesicle protein 2A, could directly suppress the Ih magnitude. Carisbamate, an anticonvulsant agent, not only inhibited the Ih amplitude but also reduced the strength of voltage-dependent hysteresis (Hys(V)) associated with Ih. Cilobradine, similar to ivabradine, inhibited the amplitude of Ih; however, it also suppressed the amplitude of delayed-rectifier K+ currents. Dexmedetomidine, an agonist of α2-adrenergic receptor, exerted a depressant action on Ih in a concentration-dependent fashion. Suppression of Ih amplitude was observed when GAL-021, a breathing control modulator, was present at a concentration exceeding 30 μM. Lutein, one of the few xanthophyll carotenoids, was able to suppress the Ih amplitude as well as to depress Hys(V)’s strength of Ih. Pirfenidone, a pyridine derivative known to be an anti-fibrotic agent, depressed the Ih magnitude in a concentration- and voltage-dependent fashion. Tramadol, a synthetic centrally active analgesic, was shown to reduce the Ih magnitude, independent of its interaction with opioid receptors. Various herbal drugs, including ent-kaurane-type diterpenoids from Croton tonkinensis, Ganoderma triterpenoids, honokiol, and pterostilbene, demonstrated efficacy in reducing the magnitude of Ih. Conversely, oxaliplatin, a platinum-based chemotherapeutic compound, was observed to effectively increase the Ih amplitude. Collectively, the regulatory effects of these compounds or herbal drugs on cellular function can be partly attributed to their perturbations on Ih. Keywords: hyperpolarization-activated cation current; current kinetics; small molecules; herbal drugs Less

Kynurenic acid (KYNA, 4-oxoquinoline-2-carboxylic acid), an intermediate of the tryptophan metabolism, has been recognized to exert different neuroactive actions; however... More

Kynurenic acid (KYNA, 4-oxoquinoline-2-carboxylic acid), an intermediate of the tryptophan metabolism, has been recognized to exert different neuroactive actions; however, the need of how it or its aminoalkylated amide derivative N-(2-(dimethylamino)ethyl)-3-(morpholinomethyl)-4-oxo-1,4-dihydroquinoline-2-carboxamide (KYNA-A4) exerts any effects on ion currents in excitable cells remains largely unmet. In this study, the investigations of how KYNA and other structurally similar KYNA derivatives have any adjustments on different ionic currents in pituitary GH3 cells and hippocampal mHippoE-14 neurons were performed by patch-clamp technique. KYNA or KYNA-A4 increased the amplitude of M-type K+ current (IK(M)) and concomitantly enhanced the activation time course of the current. The EC50 value required for KYNA- or KYNA-A4 -stimulated IK(M) was yielded to be 18.1 or 6.4 μM, respectively. The presence of KYNA or KYNA-A4 shifted the relationship of normalized IK(M)-conductance versus membrane potential to more depolarized potential with no change in the gating charge of the current. The voltage-dependent hysteretic area of IK(M) elicited by long-lasting triangular ramp pulse was observed in GH3 cells and that was increased during exposure to KYNA or KYNA-A4. In cell-attached current recordings, addition of KYNA raised the open probability of M-type K+ channels, along with increased mean open time of the channel. Cell exposure to KYNA or KYNA-A4 mildly inhibited delayed-rectifying K+ current; however, neither erg-mediated K+ current, hyperpolarization-activated cation current, nor voltage-gated Na+ current in GH3 cells was changed by KYNA or KYNA-A4. Under whole-cell, current-clamp recordings, exposure to KYNA or KYNA-A4 diminished the frequency of spontaneous action potentials; moreover, their reduction in firing frequency was attenuated by linopirdine, yet not by iberiotoxin or apamin. In hippocampal mHippoE-14 neurons, the addition of KYNA also increased the IK(M) amplitude effectively. Taken together, the actions presented herein would be one of the noticeable mechanisms through which they modulate functional activities of excitable cells occurring in vivo. Less

Oxaliplatin (OXAL) is regarded as a platinum-based anti-neoplastic agent. However, its perturbations on membrane ionic currents in neurons and neuroendocrine or endocrine... More

Oxaliplatin (OXAL) is regarded as a platinum-based anti-neoplastic agent. However, its perturbations on membrane ionic currents in neurons and neuroendocrine or endocrine cells are largely unclear, though peripheral neuropathy has been noted during its long-term administration. In this study, we investigated how the presence of OXAL and other related compounds can interact with two types of inward currents; namely, hyperpolarization-activated cation current (Ih) and membrane electroporation-induced current (IMEP). OXAL increased the amplitude or activation rate constant of Ih in a concentration-dependent manner with effective EC50 or KD values of 3.2 or 6.4 μM, respectively, in pituitary GH3 cells. The stimulation by this agent of Ih could be attenuated by subsequent addition of ivabradine, protopine, or dexmedetomidine. Cell exposure to OXAL (3 μM) resulted in an approximately 11 mV rightward shift in Ih activation along the voltage axis with minimal changes in the gating charge of the curve. The exposure to OXAL also effected an elevation in area of the voltage-dependent hysteresis elicited by long-lasting triangular ramp. Additionally, its application resulted in an increase in the amplitude of IMEP elicited by large hyperpolarization in GH3 cells with an EC50 value of 1.3 μM. However, in the continued presence of OXAL, further addition of ivabradine, protopine, or dexmedetomidine always resulted in failure to attenuate the OXAL-induced increase of IMEP amplitude effectively. Averaged current-voltage relation of membrane electroporation-induced current (IMEP) was altered in the presence of OXAL. In pituitary R1220 cells, OXAL-stimulated Ih remained effective. In Rolf B1.T olfactory sensory neurons, this agent was also observed to increase IMEP in a concentration-dependent manner. In light of the findings from this study, OXAL-mediated increases of Ih and IMEP may coincide and then synergistically act to increase the amplitude of inward currents, raising the membrane excitability of electrically excitable cells, if similar in vivo findings occur. Keywords: pituitary cell; olfactory neuron; hyperpolarization-activated cation current; membrane electroporation-induced current; oxaliplatin Less

Bisoprolol (BIS) is a selective antagonist of β1 adrenergic receptors. We examined the effects of BIS on M-type K+ currents (IK(M)) or erg-mediated K+ currents (IK(erg))... More

Bisoprolol (BIS) is a selective antagonist of β1 adrenergic receptors. We examined the effects of BIS on M-type K+ currents (IK(M)) or erg-mediated K+ currents (IK(erg)) in pituitary GH3, R1220 cells, and hippocampal mHippoE-14 cells. As GH3 cells were exposed to BIS, amplitude of IK(M) was suppressed with an IC50 value of 1.21 μM. The BIS-induced suppression of IK(M) amplitude was not affected by addition of isoproterenol or ractopamine, but attenuated by flupirtine or ivabradine. In cell-attached current, BIS decreased the open probability of M-type K+ (KM) channels, along with decreased mean opening time of the channel. BIS decreased IK(erg) amplitude with an IC50 value of 6.42 μM. Further addition of PD-118057 attenuated BIS-mediated inhibition of IK(erg). Under current-clamp conditions, BIS depolarization increased the firing of spontaneous action potentials in GH3 cells; addition of flupirtine, but not ractopamine, reversed BIS-induced firing rate. In R1220 cells, BIS suppressed IK(M); subsequent application of ML-213(Kv7.2 channel activator) reversed BIS-induced suppression of the current. In hippocampal mHippoE-14 neurons, BIS inhibited IK(M) to a greater extent compared to its depressant effect on IK(erg). This demonstrated that in pituitary cells and hippocampal neurons the presence of BIS is capable of directly and differentially suppressing IK(M) and IK(erg), despite its antagonism of β1-adrenergic receptors. Keywords: bisoprolol; M-type K+ current; M-type K+ channel. erg-mediated K+ current; membrane potential; pituitary cell Less

Nonfunctioning pituitary adenoma (NFPA) is one of the most common types of pituitary adenoma. The marine anthraquinone derivative SZ-685C has been isolated from the secon... More

Nonfunctioning pituitary adenoma (NFPA) is one of the most common types of pituitary adenoma. The marine anthraquinone derivative SZ-685C has been isolated from the secondary metabolites of the mangrove endophytic fungus Halorosellinia sp. (No. 1403) which is found in the South China Sea. Recent research has shown that SZ-685C possesses anticancer and tumor suppressive effects. The tetrazolium-based colorimetric assay (MTT assay) to investigate the different effect of the marine compound SZ-685C on the proliferation of primary human NFPA cells, rat normal pituitary cells (RPCs) and rat prolactinoma MMQ cell lines. Hoechst 33342 dye/propidium iodide (PI) double staining and fluorescein isothiocyanate-conjugated Annexin V/PI (Annexin V-FITC/PI) apoptosis assays detected an enhanced rate of apoptosis in cells treated with SZ-685C. Enhanced expression levels of caspase 3 and phosphate and tensin homolog (PTEN) were determined by Western blotting. Notably, the protein expression levels of Akt were decreased when the primary human NFPA cells were treated with SZ-685C. Here, we show that SZ-685C induces apoptosis of human NFPA cells through inhibition of the Akt pathway in vitro. The understanding of apoptosis has provided the basis for novel targeted therapies that can induce death in cancer cells or sensitize them to established cytotoxic agents and radiation therapy. Keywords: marine metabolites; SZ-685C; nonfunctioning pituitary adenomas; apoptosis Less