Fenamates block gap junction coupling and potentiate BKCa channels in guinea pig arteriolar cells

Primary Cultivation and Identification of Vascular Smooth Muscle Cells from the Spiral Modiolar Artery of Guinea Pigs

Background

This article reports a method to obtain vascular smooth muscle cells (SMCs) from the spiral modiolar artery (SMA) of guinea pigs and provides materials for related experimental studies.

Material/Methods

SMA was separated from the cochlea of guinea pigs, digested with trypsin (1.25 g/L) and allowed to adhere in a 35-mm culture dish. The morphology of the sample was investigated, and the sample was identified by immunofluorescence analysis, flow cytometry, Western blot, and RT-PCR. Cell viability was calculated using trypan blue and flow cytometry. Whole-cell patch clamp was used to record the membrane input resistance (R_input), reciprocal membrane input conductance (G_input), membrane input capacitance (C_input), and resting membrane potential (RP) of the SMCs.

Results

Microscopy results showed that the cells had typical peak–valley growth pattern. The cell growth curve was similar to an S curve, and flow cytometry results showed that the cell apoptosis rate was less than 10%. Moreover, flow cytometry, immunofluorescent staining, Western blot and RT-PCR detected the specific and intensely positive expression of cell type-specific markers α-SM-actin, SM22α, calponin and desmin. Furthermore, following properties of the P3 and P6 cells were obtained: R_input, 2611±356 and 2477±338 MΩ; G_input, 0.454±0.071 and 0.273±0.037 ns; C_input, 17.029±0.917 and 18.042±1.051 pF, and RP −20.602±1.503 and −22.192±1.905 mV.

Conclusions

Various highly purified SMCs were obtained from the SMA of guinea pigs. We provide an ideal experimental material for the study of the pathogenesis of diseases related to the circulation disturbances in the inner ear in vitro. The results can be used to evaluate the effects of drugs on vascular smooth muscle.

The role of Ca2+-activated Cl- current in tone generation in the rabbit corpus cavernosum

Rabbit corpus cavernosum smooth muscle (RCCSM) cells express ion channels that produce Ca²⁺-activated Cl^- (I_ClCa) current, but low sensitivity to conventional antagonists has made its role in tone generation difficult to evaluate. We have reexamined this question using two new generation I_ClCa blockers, T16A_inh-A01 and CaCC_inh-A01. Isolated RCCSM cells were studied using the perforated patch method. Current-voltage protocols revealed that both L-type Ca²⁺ current and I_ClCa T16A_inh-A01 and CaCC_inh-A01 (10 μM) reduced I_ClCa by ~85%, while 30 μM abolished it. L-type Ca²⁺ current was unaffected by 10 μM CaCC_inh-A01 but was reduced by 50% at 30 μM CaCC_inh-A01, 46% at 10 μM T16A_inh-A01, and 78% at 30 μM T16A_inh-A01. Both drugs reduced spontaneous isometric tension in RCCSM strips, by 60-70% at 10 μM and >90% at 30 μM. Phenylephrine (PE)-enhanced tension was also reduced (ED₅₀ = 3 μM, CaCC_inh-A01; 14 μM, T16A_inh-A01). CaCC_inh-A01 at 10 μM had little effect on 60 mM KCl contractures, though they were reduced by 30 μM CaCC_inh-A01 and T16A_inh-A01 (10 μM and 30 μM) consistent with their effects on L-type Ca²⁺ current. Both drugs also reversed the stimulatory effect of PE on intracellular Ca²⁺ waves, studied with laser scanning confocal microscopy in isolated RCCSM cells. In conclusion, although both drugs were effective blockers of I_ClCa, the effect of T16A_inh-A01 on L-type Ca²⁺ current precludes its use for evaluating the role of I_ClCa in tone generation. However, 10 μM CaCC_inh-A01 selectively blocked I_ClCa versus L-type Ca²⁺ current and reduced spontaneous and PE-induced tone, suggesting that I_ClCa is important in maintaining penile detumescence.

Effects of RMF on BKCa and Kv channels in basilar arterial smooth‑muscle cells of SHR

The current study observed the effects and investigated the mechanism of remifentanil (RMF) on the isolated cerebral basilar arteries of spontaneously hypertensive rats (SHR) and Wistar-Kyoto (WKY) rats. A pressure myograph system was used to observe and compare the effects of different concentrations of RMF (10⁻¹⁰-10⁻⁵ mol/l) on the diameter changes of freshly isolated cerebral basilar arteries, which have been pre-shrunk by phenylephrine (PE), an endothelium-independent vasoconstrictor. Vascular smooth-muscle cells of the cerebral basilar artery (BASMCs) were freshly obtained via enzymolysis. BKCa (large-conductance calcium-activated potassium channels) current (I_BKCa) and Kv (voltage-gated potassium channels) current (I_Kv) were recorded using a whole-cell patch-clamp technique. The changes in I_BKCa and I_Kv produced by different concentrations of RMF (10⁻¹⁰ to 10⁻⁵ mol/l) on the two types of rats with the holding potential of −40 mV were observed and compared. The cerebral basilar arteries of the SHR and WKY rats were relaxed by RMF in a concentration-dependent manner (P<0.05; n=5). At the same concentration, the diastolic effect of RMF on SHR was weaker than that observed in WKY rats (P<0.05, n=5). When the rats were pre-perfused with 10⁻³ mol/l of the BKCa channel blocker tetraethylammonium (TEA), the diastolic amplitudes of RMF in SHR and WKY rats were decreased, and the fitting curves shifted down (P<0.05; n=7 and 6, respectively). However, no statistically significant difference was observed with 10⁻³ mol/l of the Kv channel blocker 4-aminopyridine (4-AP; n=6 and 9, respectively; P>0.05). Outward currents were increased by RMF in both BASMCs of SHR and WKY rats in a voltage- and dose-dependent manner (P<0.05; n=6). At the same concentration, the effect of RMF on the outward currents in BASMCs of WKY rats was stronger than that on SHR (P<0.05; n=6). The enhancing effect of RMF can be partially blocked by either 10⁻³ mol/l TEA (P<0.05; n=6) or 10⁻³ mol/l 4-AP (P<0.05 or 0.01; n=6 and 9, respectively) however can be totally blocked by the mixture of TEA and 4-AP (P<0.05, n=7). RMF served a diastolic role in the cerebral basilar arteries of rats in a dose-dependent manner, likely by activating the BKCa and Kv channels. However, SHR demonstrated a less pronounced diastolic reaction to RMF than that observed in WKY rats.

Gap Junction Blockers: An Overview of their Effects on Induced Seizures in Animal Models

BACKGROUND

Gap junctions are clusters of intercellular channels allowing the bidirectional pass of ions directly into the cytoplasm of adjacent cells. Electrical coupling mediated by gap junctions plays a role in the generation of highly synchronized electrical activity. The hypersynchronous neuronal activity is a distinctive characteristic of convulsive events. Therefore, it has been postulated that enhanced gap junctional communication is an underlying mechanism involved in the generation and maintenance of seizures. There are some chemical compounds characterized as gap junction blockers because of their ability to disrupt the gap junctional intercellular communication.

OBJECTIVE

Hence, the aim of this review is to analyze the available data concerning the effects of gap junction blockers specifically in seizure models.

RESULTS

Carbenoxolone, quinine, mefloquine, quinidine, anandamide, oleamide, heptanol, octanol, meclofenamic acid, niflumic acid, flufenamic acid, glycyrrhetinic acid and retinoic acid have all been evaluated on animal seizure models. In vitro, these compounds share anticonvulsant effects typically characterized by the reduction of both amplitude and frequency of the epileptiform activity induced in brain slices. In vivo, gap junction blockers modify the behavioral parameters related to seizures induced by 4-aminopyridine, pentylenetetrazole, pilocarpine, penicillin and maximal electroshock.

CONCLUSION

Although more studies are still required, these molecules could be a promising avenue in the search for new pharmaceutical alternatives for the treatment of epilepsy.

Enhanced expression of Cx43 and gap junction communication in vascular smooth muscle cells of spontaneously hypertensive rats

Niflumic acid (NFA) is a novel gap junction (GJ) inhibitor. The aim of the present study was to investigate the effect of NFA on GJ communication and the expression of connexin (Cx) in vascular smooth muscle cells (VSMCs) of mesenteric arterioles of spontaneously hypertensive rats (SHR). Whole-cell patch clamp recording demonstrated that NFA at 1×10–4 M significantly inhibited the inward current and its effect was reversible. The time for charging and discharging of cell membrane capacitance (Cinput) reduced from 9.73 to 0.48 ms (P<0.05; n=6). Pressure myograph measurement showed that NFA at 3×10-4 M fully neutralized the contraction caused by phenylephrine. The relaxation responses of normotensive control Wistar Kyoto (WKY) rats were significantly higher, compared with those of the SHRs (P<0.05; n=6). Western blot and reverse transcription-quantitative polymerase chain reaction analyses showed that the mRNA and protein expression levels of Cx43 of the third-level branch of mesenteric arterioles of the SHRs and WKY rats were higher, compared with those of the first-level branch. The mRNA and protein expression levels of Cx43 of the primary and third-level branches of the mesenteric arterioles in the SHRs were higher, compared with those in the WKY rats (P<0.05; n=6). The mRNA levels of Cx43 in the mesenteric arterioles were significantly downregulated by NFA in a concentration-dependent manner (P<0.01; n=6). The protein levels of Cx43 in primary cultured VSMCs isolated from the mesenteric arterioles were also significantly downregulated by NFA in a concentration-dependent manner (P<0.01; n=6). These results showed that the vasorelaxatory effects of GJ inhibitors were reduced in the SHRs, which was associated with a higher protein expression level of Cx43 in the mesenteric arterioles of the SHRs. NFA also relaxed the mesenteric arterioles by reducing the expression of Cx43, which decreased blood pressure. Therefore, regulation of the expression of GJs may be a therapeutic target for the treatment of hypertension.

The enhancement of Cx45 expression and function in renal interlobar artery of spontaneously hypertensive rats at different age

BACKGROUND/AIMS

This study was designed to investigate the expression and function of gap junction protein connexin 45 (Cx45) in renal interlobar artery (RIA) of spontaneously hypertensive rats (SHR), and the association between hypertension and enhanced vasoconstrictive response in SHR.

METHODS

Western blot analysis and pressure myography were used to examine the differences in expression and function of Cx45 in vascular smooth muscle cells (VSMCs) of RIA between SHR and normotensive Wistar-Kyoto (WKY) rats.

RESULTS

Our results demonstrated that 1) whole-cell patch clamp measurements showed that the membrane capacitance and conductance of in-situ RIA VSMCs of SHR were significantly greater than those of WKY rats (p<0.05, n=6), suggesting that the coupling of gap junction between VSMCs of RIA was enhanced in SHR; 2) the KCl or phenylephrine (PE)-stimulated RIA constriction was more pronounced in SHR than that in WKY rats (p<0.05, n=10). After applying a gap junction inhibitor 18β-glycyrrhetintic acid (18β-GA), the inhibitory effect of 18β-GA on KCl or PE-induced vasoconstriction was greater in SHR (p<0.05, n=10); and 3) the expression of Cx45 in RIA of SHR was greater than that in WKY rats (p<0.05, n=3) at 4, 12 and 48 wks of age.

CONCLUSIONS

The hypertension-induced elevation of Cx45 may affect communication between VSMCs and coupling between VSMCs and endothelium, which results in an increased vasoconstrictive response in renal artery and might contribute to the development of hypertension.

Neuronal Atrophy Early in Degenerative Ataxia Is a Compensatory Mechanism to Regulate Membrane Excitability

Neuronal atrophy in neurodegenerative diseases is commonly viewed as an early event in a continuum that ultimately results in neuronal loss. In a mouse model of the polyglutamine disorder spinocerebellar ataxia type 1 (SCA1), we tested the hypothesis that cerebellar Purkinje neuron atrophy serves an adaptive role rather than being simply a nonspecific response to injury. In acute cerebellar slices from SCA1 mice, we find that Purkinje neuron pacemaker firing is initially normal but, with the onset of motor dysfunction, becomes disrupted, accompanied by abnormal depolarization. Remarkably, subsequent Purkinje cell atrophy is associated with a restoration of pacemaker firing. The early inability of Purkinje neurons to support repetitive spiking is due to unopposed calcium currents resulting from a reduction in large-conductance calcium-activated potassium (BK) and subthreshold-activated potassium channels. The subsequent restoration of SCA1 Purkinje neuron firing correlates with the recovery of the density of these potassium channels that accompanies cell atrophy. Supporting a critical role for BK channels, viral-mediated increases in BK channel expression in SCA1 Purkinje neurons improves motor dysfunction and partially restores Purkinje neuron morphology. Cerebellar perfusion of flufenamic acid, an agent that restores the depolarized membrane potential of SCA1 Purkinje neurons by activating potassium channels, prevents Purkinje neuron dendritic atrophy. These results suggest that Purkinje neuron dendritic remodeling in ataxia is an adaptive response to increases in intrinsic membrane excitability. Similar adaptive remodeling could apply to other vulnerable neuronal populations in neurodegenerative disease.

SIGNIFICANCE STATEMENT

In neurodegenerative disease, neuronal atrophy has long been assumed to be an early nonspecific event preceding neuronal loss. However, in a mouse model of spinocerebellar ataxia type 1 (SCA1), we identify a previously unappreciated compensatory role for neuronal shrinkage. Purkinje neuron firing in these mice is initially normal, but is followed by abnormal membrane depolarization resulting from a reduction in potassium channels. Subsequently, these electrophysiological effects are counteracted by cell atrophy, which by restoring normal potassium channel membrane density, re-establishes pacemaker firing. Reversing the initial membrane depolarization improved motor function and Purkinje neuron morphology in the SCA1 mice. These results suggest that Purkinje neuron remodeling in ataxia is an active compensatory response that serves to normalize intrinsic membrane excitability.