Changes in T-type calcium channel and its subtypes in overactive detrusor of the rats with partial bladder outflow obstruction

Urinary bladder smooth muscle ion channels: expression, function, and regulation in health and disease

Urinary bladder smooth muscle (UBSM), also known as detrusor smooth muscle, forms the bladder wall and ultimately determines the two main attributes of the organ: urine storage and voiding. The two functions are facilitated by UBSM relaxation and contraction, respectively, which depend on UBSM excitability shaped by multiple ion channels. In this review, we summarize the current understanding of key ion channels establishing and regulating UBSM excitability and contractility. They include excitation-enhancing voltage-gated Ca2+ (Cav) and transient receptor potential channels, excitation-reducing K+ channels, and still poorly understood Cl- channels. Dynamic interplay among UBSM ion channels determines the overall level of Cav channel activity. The net Ca2+ influx via Cav channels increases global intracellular Ca2+ concentration, which subsequently triggers UBSM contractility. Here, for each ion channel type, we describe UBSM tissue/cell expression (mRNA and protein) profiles and their role in regulating excitability and contractility of UBSM in various animal species, including the mouse, rat, and guinea pig, and, most importantly, humans. The currently available data reveal certain interspecies differences, which complicate the translational value of published animal research results to humans. This review highlights recent developments, findings on genetic knockout models, pharmacological data, reports on UBSM ion channel dysfunction in animal bladder disease models, and the very limited human studies currently available. Among all gaps in present-day knowledge, the unknowns on expression and functional roles for ion channels determined directly in human UBSM tissues and cells under both normal and disease conditions remain key hurdles in the field.

Properties of single-channel and whole cell Cl- currents in guinea pig detrusor smooth muscle cells

Multiple types of Cl^- channels regulate smooth muscle excitability and contractility in vascular, gastrointestinal, and airway smooth muscle cells. However, little is known about Cl^- channels in detrusor smooth muscle (DSM) cells. Here, we used inside-out single channel and whole cell patch-clamp recordings for detailed biophysical and pharmacological characterizations of Cl^- channels in freshly isolated guinea pig DSM cells. The recorded single Cl^- channels displayed unique gating with multiple subconductive states, a fully opened single-channel conductance of 164 pS, and a reversal potential of -41.5 mV, which is close to the E_Cl of -65 mV, confirming preferential permeability to Cl^-. The Cl^- channel demonstrated strong voltage dependence of activation (half-maximum of mean open probability, V_0.5, ~-20 mV) and robust prolonged openings at depolarizing voltages. The channel displayed similar gating when exposed intracellularly to solutions containing Ca²⁺-free or 1 mM Ca²⁺. In whole cell patch-clamp recordings, macroscopic current demonstrated outward rectification, inhibitions by 4,4'-diisothiocyano-2,2'-stilbenedisulfonic acid (DIDS) and niflumic acid, and insensitivity to chlorotoxin. The outward current was reversibly reduced by 94% replacement of extracellular Cl^- with I^-, Br^-, or methanesulfonate (MsO^-), resulting in anionic permeability sequence: Cl^->Br^->I^->MsO^-. While intracellular Ca²⁺ levels (0, 300 nM, and 1 mM) did not affect the amplitude of Cl^- current and outward rectification, high Ca²⁺ slowed voltage-step current activation at depolarizing voltages. In conclusion, our data reveal for the first time the presence of a Ca²⁺-independent DIDS and niflumic acid-sensitive, voltage-dependent Cl^- channel in the plasma membrane of DSM cells. This channel may be a key regulator of DSM excitability.

A biophysically constrained computational model of the action potential of mouse urinary bladder smooth muscle

Urinary incontinence is associated with enhanced spontaneous phasic contractions of the detrusor smooth muscle (DSM). Although a complete understanding of the etiology of these spontaneous contractions is not yet established, it is suggested that the spontaneously evoked action potentials (sAPs) in DSM cells initiate and modulate the contractions. In order to further our understanding of the ionic mechanisms underlying sAP generation, we present here a biophysically detailed computational model of a single DSM cell. First, we constructed mathematical models for nine ion channels found in DSM cells based on published experimental data: two voltage gated Ca2+ ion channels, an hyperpolarization-activated ion channel, two voltage-gated K+ ion channels, three Ca2+-activated K+ ion channels and a non-specific background leak ion channel. The ion channels' kinetics were characterized in terms of maximal conductances and differential equations based on voltage or calcium-dependent activation and inactivation. All ion channel models were validated by comparing the simulated currents and current-voltage relations with those reported in experimental work. Incorporating these channels, our DSM model is capable of reproducing experimentally recorded spike-type sAPs of varying configurations, ranging from sAPs displaying after-hyperpolarizations to sAPs displaying after-depolarizations. The contributions of the principal ion channels to spike generation and configuration were also investigated as a means of mimicking the effects of selected pharmacological agents on DSM cell excitability. Additionally, the features of propagation of an AP along a length of electrically continuous smooth muscle tissue were investigated. To date, a biophysically detailed computational model does not exist for DSM cells. Our model, constrained heavily by physiological data, provides a powerful tool to investigate the ionic mechanisms underlying the genesis of DSM electrical activity, which can further shed light on certain aspects of urinary bladder function and dysfunction.

Increased Expression of TREK-1 K+ Channel in the Dorsal Root Ganglion of Rats with Detrusor Overactivity After Partial Bladder Outlet Obstruction

Background

Changes in expression and activity of ion channels are important pathophysiological mechanisms underlying detrusor overactivity (DO) in partial bladder outlet obstruction (PBOO). The objective of this study was to examine the expression of TREK-1 channel in the bladder and central nervous system of DO rats.

Material/Methods

Thirty Sprague-Dawley rats were subjected to PBOO operations and those displaying non-voiding contractions (NVCs) in cystometry were classified as DO. Sham-operated rats without NVCs in cystometry served as controls. The expression and distribution of TREK-1 in the bladder, spinal cord, and dorsal root ganglion (DRG) were detected by real time-PCR, western blot, and immunohistochemistry.

Results

TREK-1 channel expression in the DRG was significantly increased at the mRNA level (11.20±3.762 vs. 3.209±1.505, P<0.01) and protein level (2.195±0.058 vs. 1.713±0.066, P<0.01) in DO rats as compared to control rats. However, the expression of TREK-1 mRNA in the bladder (1.380±0.810 vs. 4.206±3.827, P>0.05) and spinal cord (0.764±0.357 vs. 0.696±0.188, P>0.05) was comparable between the 2 groups. Immunohistochemistry showed enhanced immunoreactive signals of TREK-1 channel in the DRG, but not in the spinal cord and bladder.

Conclusions

TREK-1 channel was upregulated in the DRG of DO rats after chronic PBOO, which might suppress neuronal excitability and play a protective role in bladder overactivity in PBOO.

Hyperpolarization-activated cation and T-type calcium ion channel expression in porcine and human renal pacemaker tissues

Renal pacemaker activity triggers peristaltic upper urinary tract contractions that propel waste from the kidney to the bladder, a process prone to congenital defects that are the leading cause of pediatric kidney failure. Recently, studies have discovered that hyperpolarization-activated cation (HCN) and T-type calcium (TTC) channel conductances underlie murine renal pacemaker activity, setting the origin and frequency and coordinating upper urinary tract peristalsis. Here, we determined whether this ion channel expression is conserved in the porcine and human urinary tracts, which share a distinct multicalyceal anatomy with multiple pacemaker sites. Double chromagenic immunohistochemistry revealed that HCN isoform 3 is highly expressed at the porcine minor calyces, the renal pacemaker tissues, whereas the kidney and urinary tract smooth muscle lacked this HCN expression. Immunofluorescent staining demonstrated that HCN(+) cells are integrated within the porcine calyx smooth muscle, and that they co-express TTC channel isoform Cav3.2. In humans, the anatomic structure of the minor calyx pacemaker was assayed via hematoxylin and eosin analyses, and enabled the visualization of the calyx smooth muscle surrounding adjacent papillae. Strikingly, immunofluorescence revealed that HCN3(+) /Cav3.2(+) cells are also localized to the human minor calyx smooth muscle. Collectively, these data have elucidated a conserved molecular signature of HCN and TTC channel expression in porcine and human calyx pacemaker tissues. These findings provide evidence for the mechanisms that can drive renal pacemaker activity in the multi-calyceal urinary tract, and potential causes of obstructive uropathies.

Enhanced expression of TWIK-related arachidonic acid-activated K+ channel in the spinal cord of detrusor overactivity rats after partial bladder outlet obstruction

Background

Detrusor overactivity (DO) secondary to partial bladder outlet obstruction (PBOO) is closely associated with alteration of ion channels. The objective of this study is to investigate the expression of the TWIK-related arachidonic acid-activated K⁺ channel (TRAAK) in the L6-S1 spinal cord of DO rats after PBOO.

Methods

Female Sprague–Dawley rats undergoing PBOO surgery were screened for DO by cystometry. Sham-operated rats served as controls. The expression of TRAAK in the L6-S1 spinal cord was detected by real-time polymerase chain reaction, western blotting and immunohistochemistry.

Results

DO was successfully induced after chronic PBOO in rats, with an incidence rate of 62.5 %. Compared with sham-operated rats, the expression of TRAAK in the L6-S1 spinal cord of DO rats was significantly increased at the mRNA (1.886 ± 0.710 versus 0.790 ± 0.679, P < 0.05) and protein level (0.510 ± 0.087 versus 0.255 ± 0.107, P < 0.05). Immunohistochemical staining showed increased expression of TRAAK in the dorsal horn and ventral horn of the spinal cord.

Conclusions

Upregulation of TRAAK was observed in the spinal cord of DO rats after chronic PBOO, which may exert a protective effect against DO by suppressing the excitability of neurons.

Central role of the BK channel in urinary bladder smooth muscle physiology and pathophysiology

The physiological functions of the urinary bladder are to store and periodically expel urine. These tasks are facilitated by the contraction and relaxation of the urinary bladder smooth muscle (UBSM), also known as detrusor smooth muscle, which comprises the bladder wall. The large-conductance voltage- and Ca(2+)-activated K(+) (BK, BKCa, MaxiK, Slo1, or KCa1.1) channel is highly expressed in UBSM and is arguably the most important physiologically relevant K(+) channel that regulates UBSM function. Its significance arises from the fact that the BK channel is the only K(+) channel that is activated by increases in both voltage and intracellular Ca(2+). The BK channels control UBSM excitability and contractility by maintaining the resting membrane potential and shaping the repolarization phase of the spontaneous action potentials that determine UBSM spontaneous rhythmic contractility. In UBSM, these channels have complex regulatory mechanisms involving integrated intracellular Ca(2+) signals, protein kinases, phosphodiesterases, and close functional interactions with muscarinic and β-adrenergic receptors. BK channel dysfunction is implicated in some forms of bladder pathologies, such as detrusor overactivity, and related overactive bladder. This review article summarizes the current state of knowledge of the functional role of UBSM BK channels under normal and pathophysiological conditions and provides new insight toward the BK channels as targets for pharmacological or genetic control of UBSM function. Modulation of UBSM BK channels can occur by directly or indirectly targeting their regulatory mechanisms, which has the potential to provide novel therapeutic approaches for bladder dysfunction, such as overactive bladder and detrusor underactivity.

Changes in store-operated calcium channels in rat bladders with detrusor overactivity

OBJECTIVE

To investigate the regulation of intracellular store-operated calcium channels (SOCCs) in detrusor overactivity (DO) during detrusor function changes in Sprague-Dawley rats.

METHODS

Sixty female Sprague-Dawley rats were randomized into control and DO groups. The contraction of the smooth muscle of the bladder was evaluated in vivo using smooth muscle strips. Changes in intracellular calcium ions were observed using confocal microscopy with preload fluo-4 AM, the SOCC agonist cyclopiazonic acid (CPA; 10 μM) and inhibitor SKF-96365 (10 μM). Cell currents were recorded with the whole-cell patch-clamp technique.

RESULTS

The in vitro frequencies of bladder smooth muscle contraction were significantly different (P <.05) between the DO and control groups, and the amplitudes were not significantly different (P >.05). The changes in intracellular calcium ions and current density were significantly different between the 2 groups (P <.05).

CONCLUSION

SOCCs were involved in DO and caused variations in muscle contraction.

T-type Ca2+ channels and the urinary and male genital tracts

T-type Ca(2+) channels are widely expressed throughout the urinary and male genital tracts, generally alongside L-type Ca(2+) channels. The use of pharmacological blockers of these channels has suggested functional roles in all regions, with the possible exception of the ureter. Their functional expression is apparent not just in smooth muscle cells but also in interstitial cells that lie in close proximity to muscle, nerve and epithelial components of these tissues. Thus, T-type Ca(2+) channels can contribute directly to modulation of muscle function and indirectly to changes of epithelial and nerve function. T-type Ca(2+) channel activity modulates phasic contractile activity, especially in conjunction with Ca(2+)-activated K(+) channels, and also to agonist-dependent responses in different tissues. Upregulation of channel density occurs in pathological conditions associated with enhanced contractile responses, e.g. overactive bladder, but it is unclear if this is causal or a response to the pathological state. Moreover, T-type Ca(2+) channels may have a role in the development of prostate tumours regulating the secretion of mitogens from neuroendocrine cells. Although a number of selective channel blockers exist, their relative selectivity over L-type Ca(2+) channels is often low and makes evaluation of T-type Ca(2+) channel function in the whole organism difficult.

Changes in the function and expression of T-type and N-type calcium channels in the rat bladder after bladder outlet obstruction

PURPOSE

We evaluated possible changes in the function and expression of T-type and N-type Ca(2+) channels in the bladder of rats with bladder outlet obstruction.

MATERIALS AND METHODS

Female Sprague Dawley® rats were divided into a group with bladder outlet obstruction created by partial urethral ligation and a sham operated group. Six weeks postoperatively we determined the mRNA expression of T-type and N-type Ca(2+) channels in the bladder, dorsal root ganglion and spinal cord. We also cystometrically investigated expression by intravenous administration of the T-Ca blocker RQ-00311610 or the N-type Ca(2+) channel blocker ω-conotoxin GVIA. We then performed in vitro functional studies of detrusor strips using these blockers.

RESULTS

mRNA expression of T-type Ca(2+) channels in the bladder detrusor and mucosa layers, and the spinal cord dorsal horn, and N-type Ca(2+) channels in the whole bladder and detrusor layer, and the spinal cord dorsal horn was greater in the obstructed group than the sham operated group. In obstructed rats bladder capacity and voided volume increased after RQ-00311610 administration but the number of nonvoiding contractions decreased after ω-conotoxin GVIA administration. Detrusor strips from obstructed rats showed weaker contractile responses to electrical field stimulation, particularly in regard to the purinergic component. ω-Conotoxin GVIA suppressed electrical field stimulation induced contractions only in the detrusor of obstructed rats, especially the cholinergic component.

CONCLUSIONS

Blocking T-type Ca(2+) channels increased bladder capacity while N-type Ca(2+) channel blockade inhibited nonvoiding contractions in rats with bladder outlet obstruction. Decreased bladder efferent neurotransmission occurred after bladder outlet obstruction, predominantly in its purinergic component and detrusor contractions via cholinergic neurotransmission were activated in a compensatory manner, probably via N-type Ca(2+) channel up-regulation.

Identification of T-type calcium channels in the interstitial cells of Cajal in rat bladder

OBJECTIVE

To investigate the expression and function of T-type calcium channels in the interstitial cells of Cajal in rat bladders.

METHODS

Bladders were harvested from Sprague-Dawley rats. The expression of T-type calcium channels subtypes (α1G, α1H, and α1I) in interstitial cells of Cajal were identified by double-labeled immunofluorescence analysis and reverse transcription-polymerase chain reaction analysis in whole mount preparations of rat bladders. The function of T-type calcium channels in freshly isolated interstitial cells of Cajal was assessed by detecting the changes of intracellular calcium ([Ca(2+)](i)) with preloading fluo-3 AM, and by evaluating the changes of the phasic contractions of rat bladder strips after treating with mibefradil and glivec.

RESULTS

Three T-type calcium channels subtypes, α1G, α1H, and α1I, colocalized with c-kit in bladder interstitial cells of Cajal by double-labeled immunofluorescence analysis, and this was confirmed using reverse transcription-polymerase chain reaction. The T-type calcium channels selective blocker, mibefradil (1 μM), significantly decreased the intracellular calcium concentration ([Ca(2+)](i)) in isolated interstitial cells of Cajal (P < .01) and inhibited the spontaneous phasic contraction of bladder strips (P < .01). Moreover, the c-kit receptor blocker, glivec, significantly decreased the [Ca(2+)](i) of interstitial cells of Cajal further (P < .01) and the spontaneous phasic contraction of bladder strips.

CONCLUSION

T-type calcium channel subtypes were confirmed to colocalize in interstitial cells of Cajal in rats bladders, which might participate in the spontaneous activity of interstitial cells of Cajal and phasic contractions of bladder strips by modulating [Ca(2+)](i) in interstitial cells of Cajal.

Identification of a hyperpolarization-activated cyclic nucleotide-gated channel and its subtypes in the urinary bladder of the rat

OBJECTIVE

To investigate the distribution and effects of hyperpolarization-activated cyclic nucleotide-gated (HCN) channel and its isoforms in bladder, especially in bladder interstitial cells of Cajal (ICC).

METHODS

Four HCN isoforms were detected in bladder tissue from rats using reverse transcription-polymerase chain reaction and Western blotting. The HCN1 subtype was observed in bladder ICCs by double-labeled fluorescence. The effect of the HCN blocker, ZD7288, was investigated using the bladder smooth muscle strip test.

RESULTS

HCN1-4 isoforms were all identified in bladder ICCs using reverse transcription-polymerase chain reaction and Western blotting. Based on our semiquantitative analysis, HCN1 was found to be the most prominent isoform. The expression of HCN1 was confirmed in bladder ICCs by double-labeled fluorescence through colabeling of HCN1 and kit (CD117). ZD7288 significantly decreased the bladder excitation.

CONCLUSION

All 4 HCN channel isoforms exist in the bladder, and they affect the bladder excitation, presumably via bladder ICCs.

Role of potassium ion channels in detrusor smooth muscle function and dysfunction

Contraction and relaxation of the detrusor smooth muscle (DSM), which makes up the wall of the urinary bladder, facilitates the storage and voiding of urine. Several families of K(+) channels, including voltage-gated K(+) (K(V)) channels, Ca(2+)-activated K(+) (K(Ca)) channels, inward-rectifying ATP-sensitive K(+) (K(ir), K(ATP)) channels, and two-pore-domain K(+) (K(2P)) channels, are expressed and functional in DSM. They control DSM excitability and contractility by maintaining the resting membrane potential and shaping the action potentials that determine the phasic nature of contractility in this tissue. Defects in DSM K(+) channel proteins or in the molecules involved in their regulatory pathways may underlie certain forms of bladder dysfunction, such as overactive bladder. K(+) channels represent an opportunity for novel pharmacological manipulation and therapeutic intervention in human DSM. Modulation of DSM K(+) channels directly or indirectly by targeting their regulatory mechanisms has the potential to control urinary bladder function. This Review summarizes our current state of knowledge of the functional role of K(+) channels in DSM in health and disease, with special emphasis on current advancements in the field.

Effects of bladder outlet obstruction on properties of Ca2+-activated K+ channels in rat bladder

In this study, we investigated the effects of bladder outlet obstruction (BOO) on the expression and function of large conductance (BK) and small conductance (SK) Ca(2+)-activated K(+) channels in detrusor smooth muscle. The bladder from adult female Sprague-Dawley rats with 6-wk BOO were used. The mRNA expression of the BK channel alpha-subunit, beta1-, beta2-, and beta4-subunits and SK1, SK2, and SK3 channels were investigated using real-time RT-PCR. All subunits except for the BK-beta2, SK2, and SK3 channels were predominantly expressed in the detrusor smooth muscle rather than in the mucosa. The mRNA expression of the BK channel alpha-subunit was not significantly changed in obstructed bladders. However, the expression of the BK channel beta1-subunit and the SK3 channel was remarkably increased in obstructed bladders. On the other hand, the expression of the BK channel beta4-subunit was decreased as the severity of BOO-induced bladder overactivity progressed. In detrusor smooth muscle strips from obstructed bladders, blockade of BK channels by iberiotoxin (IbTx) or charybdotoxin (CTx) and blockade of SK channels by apamin increased the amplitude of spontaneous contractions. These blockers also increased the contractility and affinity of these strips for carbachol during cumulative applications. The facilitatory effects elicited by these K(+) channel blockers were larger in the strips from obstructed bladders compared with control bladders. These results suggest that long-term exposure to BOO for 6 wk enhances the function of both BK and SK types of Ca(2+)-activated K(+) channels in the detrusor smooth muscle to induce an inhibition of bladder contractility, which might be a compensatory mechanism to reduce BOO-induced bladder overactivity.

Role of TREK-1 potassium channel in bladder overactivity after partial bladder outlet obstruction in mouse

PURPOSE

Mouse models of partial bladder outlet obstruction cause bladder hypertrophy. Expression of a number of ion channels is altered in hypertrophic detrusor muscle, resulting in bladder dysfunction. We determined whether mechanosensitive TREK-1 channels are present in the murine bladder and whether their expression is altered in partial bladder outlet obstruction, resulting in abnormal filling responses.

MATERIALS AND METHODS

Partial bladder outlet obstruction was surgically induced in CD-1 mice and the mice recovered for 14 days. Cystometry was done to evaluate bladder pressure responses during filling at 25 microl per minute in partial bladder outlet obstruction mice and sham operated controls. TREK-1 channel expression was determined at the mRNA and protein levels by quantitative reverse transcriptase-polymerase chain reaction and Western blotting, respectively, and localized in the bladder wall using immunohistochemistry.

RESULTS

Obstructed bladders showed about a 2-fold increase in weight vs sham operated bladders. TREK-1 channel protein expression on Western blots from bladder smooth muscle strip homogenates was significantly decreased in obstructed mice. Immunohistochemistry revealed a significant decrease in TREK-1 channel immunoreactivity in detrusor smooth muscle in obstructed mice. On cystometry the TREK-1 channel blocker L-methioninol induced a significant increase in premature contractions during filling in sham operated mice. L-methioninol had no significant effect in obstructed mice, which showed an overactive detrusor phenotype.

CONCLUSIONS

TREK-1 channel down-regulation in detrusor myocytes is associated with bladder overactivity in a murine model of partial bladder outlet obstruction.

Beta-adrenergic relaxation of mouse urinary bladder smooth muscle in the absence of large-conductance Ca2+-activated K+ channel

In urinary bladder smooth muscle (UBSM), stimulation of beta-adrenergic receptors (beta-ARs) leads to activation of the large-conductance Ca2+-activated K+ (BK) channel currents (Petkov GV and Nelson MT. Am J Physiol Cell Physiol 288: C1255-C1263, 2005). In this study we tested the hypothesis that the BK channel mediates UBSM relaxation in response to beta-AR stimulation using the highly specific BK channel inhibitor iberiotoxin (IBTX) and a BK channel knockout (BK-KO) mouse model in which the gene for the pore-forming subunit was deleted. UBSM strips isolated from wild-type (WT) and BK-KO mice were stimulated with 20 mM K+ or 1 microM carbachol to induce phasic and tonic contractions. BK-KO and WT UBSM strips pretreated with IBTX had increased overall contractility, and UBSM BK-KO cells were depolarized with approximately 12 mV. Isoproterenol, a nonspecific beta-AR agonist, and forskolin, an adenylate cyclase activator, decreased phasic and tonic contractions of WT UBSM strips in a concentration-dependent manner. In the presence of IBTX, the concentration-response curves to isoproterenol and forskolin were shifted to the right in WT UBSM strips. Isoproterenol- and forskolin-mediated relaxations were enhanced in BK-KO UBSM strips, and a leftward shift in the concentration-response curves was observed. The leftward shift was eliminated upon PKA inhibition with H-89, suggesting upregulation of the beta-AR-cAMP pathway in BK-KO mice. These results indicate that the BK channel is a key modulator in beta-AR-mediated relaxation of UBSM and further suggest that alterations in BK channel expression or function could contribute to some pathophysiological conditions such as overactive bladder and urinary incontinence.

Altered expression of calcium-activated K and Cl channels in detrusor overactivity of rats with partial bladder outlet obstruction

OBJECTIVE

To evaluate the activity of large- and small-conductance calcium-activated potassium channels (BKCa, SKCa) and calcium-activated chloride channels (ClCa) in detrusor overactivity (DO) cells after partial bladder outlet obstruction (PBOO) in rats.

MATERIALS AND METHODS

Thirteen female Wistar rats with DO caused by PBOO were studied simultaneously with eight sham-operated rats. The expression of KCa and ClCa channels was assessed by reverse transcription-polymerase chain reaction, and the function of the two groups compared.

RESULTS

In the DO cells the expression of BKCa, SKCa2 and SKCa3 was lower, and that of ClCa channels higher, than in the control group cells. Using confocal laser scanning microscopic analysis, the function of BKCa and SKCa channels was suppressed, and that of ClCa channels was enhanced in DO group cells. KCa and ClCa effectors altered the cell membrane potentials more significantly in the DO cells than in the control cells, indicating a decrease in KCa and an increase in ClCa in DO group in either iso- or hypo-osmolar medium. Moreover, the change in BKCa, SKCa and ClCa channel activators in DO cells showed a more excitable state in hypo-osmolar medium than in iso-osmolar medium.

CONCLUSION

In DO myocytes after PBOO, the expression and function of KCa channels were decreased, and those of ClCa channels increased. These changes all provoke greater cell excitability, and could partly account for the DO.