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Mechanosensitive ion channels (MSCs) are key molecules in the mechano-electrical transduction of arterial baroreceptors. Among them, acid-sensing ion channel 2 (ASIC2) and transient receptor potential vanilloid subfamily member 1 (TRPV1) have been studied extensively and documented to play important roles. In this study, experiments using aortic arch–aortic nerve preparations isolated from rats revealed that both ASIC2 and TRPV1 are functionally necessary, as blocking either abrogated nearly all pressure-dependent neural discharge. However, whether ASIC2 and TRPV1 work in coordination remained unclear. So we carried out cell-attached patch-clamp recordings in HEK293T cells co-expressing ASIC2 and TRPV1 and found that inhibition of ASIC2 completely blocked stretch-activated currents while inhibition of TRPV1 only partially blocked these currents. Immunofluorescence staining of aortic arch–aortic adventitia from rats showed that ASIC2 and TRPV1 are co-localized in the aortic nerve endings, and co-immunoprecipitation assays confirmed that the two proteins form a compact complex in HEK293T cells and in baroreceptors. Moreover, protein modeling analysis, exogenous co-immunoprecipitation assays, and biotin pull-down assays indicated that ASIC2 and TRPV1 interact directly. In summary, our research suggests that ASIC2 and TRPV1 form a compact complex and function synergistically in the mechano-electrical transduction of arterial baroreceptors. The model of synergism between MSCs may have important biological significance beyond ASIC2 and TRPV1. SUPPLEMENTARY INFORMATION: The online version contains supplementary material available at 10.1007/s12264-021-00737-1.

The present study was aimed to establish a simple and robust protocol that was more suitable for sorting discharges of the arterial baroreceptor. Oligo-unit (≤ 5) baroreceptor discharges were recorded in vitro from fine filaments of the rabbit carotid sinus nerve. Different time windows, covering the fast phase only or both the fast and slow phases of the spike were used to extract spike event data for sorting. Three measurements focusing on the fast phase of spikes—the maximum slope in the ascending limb from the half amplitude to the peak, the peak amplitude, and the width of the spike at the half amplitude—were selected as a feature set. The performance of this measurement-based analysis with subsequent K-means algorithm (MBAKM) in sorting oligo-unit discharges was compared with the performance of principal component analysis followed by K-means (PCAKM) and template matching (TM). The present study proved that: (1) MBAKM was more discriminative with less intervention than PCAKM and TM in determining the number of clusters and cluster attributions of spikes; (2) there was a higher consistency (larger intersection set) among the three algorithms with narrow windows of 0.45–0.65 ms than with 1.45 ms window. This study suggested that discriminative features were embodied in the fast phase of spikes and the oligo-unit discharges of baroreceptors could be sorted more robustly and accurately with less intervention by MBAKM than by PCAKM and TM. MBAKM with narrow time window would be promising in further studying baroreceptors and multiunit discharges from other neural structures.

Allium sativum L. (DaSuan in Mandarin) is a traditional Chinese herb that has been used to prevent and heal cardiovascular diseases.To study the effects of allitridi (an active constituent of Allium sativum L.) and amiodarone on the conduction system and on reverse use-dependence in the isolated hearts of normal rats and rats with myocardial infarction (MI).Male Sprague Dawley rats, with a ligated left anterior descending coronary artery, were used as myocardial infarction models to investigate the biological effects of the traditional Chinese herb. A single-phase electrode assay and isolated heart perfusion administration methods were employed to study and compare the electrophysiological effects of allitridi and amiodarone on normal and MI rats. Monophasic action potential (MAP) in vitro, effective refractory period (ERP) and monophasic action potential duration (MAPD)/ERP were measured to investigate reverse use-dependence (RUD) with allitridi and amiodarone. Moreover, bundle maps and heart rates were analyzed to evaluate the electrophysiological effects of allitridi on the conduction system of the cardiac muscles. Coronary flow was used to study the beneficial effects of the two drugs on the bundle of His in myocardial infraction.(1) Allitridi and amiodarone can reduce the infarction model of the His bundle (A-H, H-V) conduction and cardiac sinus rhythm in normal rats and isolated rat hearts. After washing in physiological solution (AK-H) for 15 min, the allitridi group partially recovered, but the amiodarone group did not recover. (2) Allitridi and amiodarone had no significant effects on the change of MAPD(90) or ERP in normal and MI rat hearts at different pacing frequencies (200, 250 and 300 beats/min), which indicated no RUD. In addition, the effects of allitridi on prolonging MAPD(90) and ERP were weaker than those of amiodarone (P0.01). The effects of allitridi on myocardial repolarization and its variation rate were also weaker than those of amiodarone (P0.01). However, the prolonged administration of allitridi still did not cause RUD. Allitridi and amiodarone can significantly increase the ERP/APD(90) rate of the isolated heart ventricles of normal rats and rats with MI.We propose that allitridi and amiodarone have similar effects on the cardiac conduction system and on the electrophysiology without RUD, which may be the result of the use of multi-channel blockers, such as calcium channel blockers and IKr and IKs channel blockers. Allitridi may be a promising antiarrythmic drug.

Stretch sensitivity of Ca2+-activated large-conductance K+ channels (BKCa) has been observed in a variety of cell types and considered to be a potential mechanism in mechanoelectric transduction (MET). Mechanical stress is a major stimulator for the smooth muscle in the gastrointestinal (GI) tract. However, much about the role and mechanism of MET in GI smooth muscles remains unknown. The BKCa shows a functional diversity due to intensive Slo I alternative splicing and different α/β-subunit assembly in various cells. The stress-regulated exon (STREX) insert is suggested to be an indispensable domain for the mechanosensitivity of BKCa. The purpose of this study was to determine whether the BKCa in colonic myocytes of the adult mouse is sensitive to mechanical stimulation and whether the STREX insert is a crucial segment for the BKCa mechanosensitivity. The α- and β1-subunit mRNAs and the α-subunit protein of the BKCa channels were detected in the colonic muscularis. We found that the BKCa STREX-lacking variant was abundantly expressed in the smooth muscle, whereas the STREX variant was not detectable. We demonstrated that the STREX-lacking BKCa channels were also sensitive to membrane stretch. We suggest that in addition to the STREX domain, there are other additional structures in the channel responsible for mechanically coupling with the cell membrane.

Transient stretching of the ventricle can trigger arrhythmias and evoke ventricular fibrillation, especially when the stimulation occurs in the vulnerable period. To explore the sensitivity of small hearts we used a commercial pressure servo to study the kinetic relationship of left ventricular pressure to excitability and arrhythmias in the rat heart. Stimulation protocols were readily composed on the computer and programmed to vary the stimulus amplitude and timing relative to pacing. The pressure-induced premature ventricular excitations were similar to those observed in larger hearts, but the convenience of using small hearts allows the use of inexpensive transgenic animals to explore the molecular basis of transduction.

Growing evidence indicates that transient receptor potential canonical (TRPC) channels play important roles in various Ca2+-mediated physiological and pathophysiological processes, including development. Many types of TRPC proteins are expressed in the heart. However, limited data are available comparing the expression and localization among TRPC proteins in the ventricular myocyte at various developmental stages. Our purpose is to investigate the expression and localization profile of TRPC proteins in ventricular myocytes of fetal (18.5 days), neonatal (< 24 h after birth) and adult (8 week old) rats. Western blotting, immunofluorescence and confocal laser scanning microscopy were employed. TRPC1/3-6 proteins were expressed in the rat ventricle throughout the three developmental stages. The expression profile of TRPC1/3/4 in the ventricle followed an upward trend from the fetus to the adult. By contrast, TRPC6 in the ventricle was expressed at the highest level in the fetal group and was sharply down-regulated immediately after birth. TRPC5 expression in the ventricle did not change significantly during the three stages. TRPC1/3/5/6 proteins were localized to the T-tubule and TRPC1/3/4/6 to intercalated disks in adult myocytes. The wide spatiotemporal overlap and dynamic regulation of TRPC expression in ventricular myocytes indicates potential complex combinations and redundancy of native TRPC proteins in the heart and gives important clues for further investigations into the exact subunit compositions and functional properties of native TRPC channels in the heart.

Cardiac KATP channels link metabolism with electrical activity. They are implicated in arrhythmias, secretion of atrial natriuretic peptide and protection of the heart from hypertrophy and failure. These processes may involve mechanosensitivity. KATP channels can be activated by mechanical stimulation and disrupting the cortical actin increases the activity. We propose that KATP channels are modulated by local bilayer tension and this tension is affected by cortical F-actin. Here we measured KATP background activity and stretch sensitivity with inside-out patches of rat ventricular myocytes before and after disrupting F-actin. Disrupting F-actin potentiated background activity but did not influence the slope sensitivity in the semilog relationship of NPo vs. suction that is a measure of the change in dimensions between closed and open states. Thus actin alters prestress on the channel probably by parallel elastic sharing of mean cortical tension with the bilayer.

Transient stretching of the ventricle can trigger arrhythmias and evoke ventricular fibrillation, especially when the stimulation occurs in the vulnerable period. To explore the sensitivity of small hearts we used a commercial pressure servo to study the kinetic relationship of left ventricular pressure to excitability and arrhythmias in the rat heart. Stimulation protocols were readily composed on the computer and programmed to vary the stimulus amplitude and timing relative to pacing. The pressure-induced premature ventricular excitations were similar to those observed in larger hearts, but the convenience of using small hearts allows the use of inexpensive transgenic animals to explore the molecular basis of transduction.

We utilized selective carotid body (CB) perfusion while changing inspired O2 fraction in arterial isocapnia to characterize the non-CB chemoreceptor ventilatory response to changes in arterial PO2 (PaO2) in awake goats and to define the effect of varying levels of CB PO2 on this response. Systemic hyperoxia (PaO2 greater than 400 Torr) significantly increased inspired ventilation (VI) and tidal volume (VT) in goats during CB normoxia, and systemic hypoxia (PaO2 = 29 Torr) significantly increased VI and respiratory frequency in these goats. CB hypoxia (CB PO2 = 34 Torr) in systemic normoxia significantly increased VI, VT, and VT/TI; the ventilatory effects of CB hypoxia were not significantly altered by varying systemic PaO2. We conclude that ventilation is stimulated by systemic hypoxia and hyperoxia in CB normoxia and that this ventilatory response to changes in systemic O2 affects the CB O2 response in an additive manner.

The present study was designed to observe the properties of swelling-activated chloride channel (ICl.swell) in mouse cardiac myocytes using patch clamp techniques. In whole-cell recordings, hypotonic solution activated a chloride current that exhibited outward rectification, weak voltage-dependent inactivation, and anion selectivity with permeability sequence of I-Br-Cl-. The current was sensitive to Cl- channel blockers tamoxifen, NPPB and DIDS. In single-channel recordings, cell swelling activated a single channel current which showed outward rectification with open probability of 0.76 +/- 0.08 and conductance of 38.1 +/- 2.5 pS at +100 mV under [Cl-] symmetrical condition. I-V relation revealed the reversal potential as expected for a Cl(-)-selective channel. These results suggested that in mouse cardiac myocytes, swelling-activated, outward rectifying chloride channel with a single channel conductance of 38.1 +/- 2.5 pS (at +100 mV under [Cl-] symmetrical condition) underlies the volume regulatory Cl- channel.

The effect of mechanical stress on the heart’s electrical activity has been termed mechanoelectric feedback. The response to stretch depends upon the magnitude and the waveform of the stimulus, and upon the timing relative to the cardiac cycle. Stretch-activated ion channels (SACs) have been regarded as the most likely candidates for serving as the primary transducers of mechanical stress. We explored the steady state and dynamic responses of single channels in adult rat atrial cells using the patch clamp with a pressure clamp. Surprisingly, we only observed K + -selective SACs, probably of the 2P domain family. The channels were weakly outward rectifying with flickery bursts. In cell attached mode, the mean conductance was 74714 and 65716 pS for +60 and � 60 mV, respectively (140 mM [K + ]out, 2 mM [Mg 2+ ]out and 0 mM [Ca 2+ ]out). The latency of the response to pressure steps was 50–100 ms and the time to peak B400 ms. About half of the channels in cell-attached patches showed adaptation/inactivation where channel activity declined to a plateau of 20–30% of peak in B1 s. The time dependent behavior of these SACs is generally consistent with whole-cell currents observed in chick and rat ventricular cells, although the net current was outward rather than inward. r 2003 Published by Elsevier Science Ltd.