The actions of extracellular H+ on the electrophysiological properties of isolated human detrusor smooth muscle cells

Preparation and Utilization of Freshly Isolated Human Detrusor Smooth Muscle Cells for Characterization of 9-Phenanthrol-Sensitive Cation Currents

Detrusor smooth muscle (DSM) cells present within the urinary bladder wall ultimately facilitate urine storage and voiding. Preparation of the viable, fresh, and isolated DSM cells presents an important technical challenge whose achievement provides optimal cells for subsequent functional and molecular studies. The method developed and elaborated herein, successfully used by our group for over a decade, describes dissection of human urinary bladder specimens obtained from open bladder surgeries followed by an enzymatic two-step treatment of DSM pieces and mechanical trituration to obtain freshly isolated DSM cells. The initial step involves dissection to separate the DSM layer (also known as muscularis propria) from mucosa (urothelium, lamina propria, and muscularis mucosa) and the adjacent connective, vascular, and adipose tissues present. The DSM is then cut into pieces (2-3 mm x 4-6 mm) in nominal Ca2+-containing dissection/digestion solution (DS). DSM pieces are next transferred to and sequentially treated separately with DS containing papain and collagenase at ~37 °C for 30-45 min per step. Following washes with DS containing enzyme-free bovine serum and trituration with a fire-polished pipette, the pieces release single DSM cells. Freshly isolated DSM cells are ideally suited for patch-clamp electrophysiological and pharmacological characterizations of ion channels. Specifically, we show that the TRPM4 channel blocker 9-phenanthrol reduces voltage-step evoked cation currents recorded with the amphotericin-B perforated patch-clamp approach. DSM cells can also be studied by other techniques such as single cell RT-PCR, microarray analysis, immunocytochemistry, in situ proximity ligation assay, and Ca2+ imaging. The main advantage of utilizing single DSM cells is that the observations made relate directly to single cell characteristics revealed. Studies of freshly isolated human DSM cells have provided important insights characterizing the properties of various ion channels including cation-permeable in the urinary bladder and will continue as a gold standard in elucidating DSM cellular properties and regulatory mechanisms.

Functional and molecular identification of pH-sensitive K+ channels in murine urinary bladder smooth muscle

OBJECTIVE

To examine the role of pH-sensitive K(+) channels in setting the resting membrane potential in murine bladder smooth muscle, as bladder contractility is influenced by the resting membrane potential, which is mainly regulated by background K(+) conductances.

MATERIALS AND METHODS

Using conventional microelectrode recordings, isometric tension measurements, patch-clamp recordings, reverse transcription-polymerase chain reaction (RT-PCR), Western blotting and immunohistochemistry, we assessed bladder smooth muscle cells and tissues.

RESULTS

Acidic pH (pH 6.5) depolarized the resting membrane potential of murine bladder smooth muscles and increased muscle tone and contractility. The pH-induced changes were not abolished by neuronal blockers or classical K(+)-channel antagonists. Lidocaine (1 mM) and bupivacaine (100 microm) mimicked the effects of acidifying the external solution, and in the presence of lidocaine no further increase in contractility was induced by reducing the pH to 6.5. Voltage-clamp experiments on freshly dispersed bladder myocytes showed that pH 6.5 decreased the outward current. Pre-treatment of bladder myocytes with the classical K(+) antagonists tetraethylammonium (10 mm), 4-aminopyridine (5 mM), glibenclamide (10 microm) or apamin (300 nM) did not inhibit the effects of low pH on outward current. However, treatment with lidocaine (1 mM) abolished the effects of acidic pH on outward current. RT-PCR showed the expression of the acid-sensitive K(+) channel (TASK)-1 and TASK-2 gene transcripts in murine bladder, and immunohistochemistry and Western blot analysis showed TASK-1 and TASK-2 channel expression and distribution in smooth muscle tissues and cells.

CONCLUSION

TASK channels are expressed in bladder smooth muscle and contribute to the basal K(+) conductances responsible for resting membrane potential.

Effects of cold storage on the function and morphology of isolated urinary bladder in rat

AIMS

We investigated the effects of 24- and 48-hr storage at 4 degrees C in Krebs solution on the function and morphology of isolated, rat urinary bladders.

METHODS

Strips of bladder were obtained from eight male Sprague-Dawley rats. Six strips were harvested from each bladder and randomized to storage for 24 or 48 hr at 4 degrees C in Krebs solution or examination immediately after harvest. Contractile responses of the strips to potassium chloride (KCl), electric field stimulation (EFS), adenosine 5'-triphosphate (ATP) and carbamylcholine (CCh) were assessed. Histological examination of the bladder strips was performed. The pO(2), pCO(2), and pH of the solution in each storage container were measured at each storage time point.

RESULTS

Cold storage induced a significant decrease in the amplitude of contraction in response to KCl and EFS after 24 or 48 hr of storage compared with control. The response of the bladder strips to ATP and CCh was significantly reduced after 48-hr storage compared with control, but not 24-hr storage. The pO(2) and pCO(2) decreased after cold storage. The pH increased after 24 hr of storage and remained stable between 24 and 48 hr of storage. Histological evaluation of the strips showed tissue swelling after 24 and 48 hr of storage.

CONCLUSIONS

These results suggest that the morphology and function of bladder strips stored for 24 to 48 hr at 4 degrees C in Krebs solution undergo significant changes. Further studies are needed to assess the allowable time for storage of bladder tissue.

Urinary bladder contraction and relaxation: physiology and pathophysiology

The detrusor smooth muscle is the main muscle component of the urinary bladder wall. Its ability to contract over a large length interval and to relax determines the bladder function during filling and micturition. These processes are regulated by several external nervous and hormonal control systems, and the detrusor contains multiple receptors and signaling pathways. Functional changes of the detrusor can be found in several clinically important conditions, e.g., lower urinary tract symptoms (LUTS) and bladder outlet obstruction. The aim of this review is to summarize and synthesize basic information and recent advances in the understanding of the properties of the detrusor smooth muscle, its contractile system, cellular signaling, membrane properties, and cellular receptors. Alterations in these systems in pathological conditions of the bladder wall are described, and some areas for future research are suggested.

Mitochondrial metabolism in the rat during bladder regeneration induced by small intestinal submucosa

OBJECTIVE

To assess mitochondrial metabolism of bladder tissue induced by small-intestinal submucosa (SIS), by comparing the mitochondrial enzyme metabolism in this tissue with that in normal bladder tissue and thus evaluate intracellular normality.

MATERIAL AND METHODS

In all, 70 rats were grouped into healthy controls (10), surgical controls with a simple bladder incision (15) and rats treated by partial cystectomy with replacement by the SIS graft (45). At 1, 3 and 6 months the rats were killed, the enzymes of mitochondrial respiratory chain complexes assayed, and the respiration of permeabilized bladder fibres assessed using polarographic analysis.

RESULTS

The enzyme activities of control and treated rats at 3 months were identical. The results from the polarographic analysis of respiration were also similar to that in normal tissue apart from a decrease in the number of mitochondria. Histologically, there was complete regeneration at 6 months.

CONCLUSION

After a phase of inflammation the bladder regenerates after a patch is placed. The new tissue has the same enzymatic and histological features as normal bladder tissue.

Differential effects of acidosis, high potassium concentrations, and metabolic inhibition on noradrenaline release and its presynaptic muscarinic regulation

It was the aim of the present study to characterize the effect of single components of ischaemia, such as inhibition of aerobic and anaerobic energy production by combined anoxic and glucose-free perfusion (metabolic inhibition), high extracellular potassium concentrations (hyperkalaemia), and acidosis, on (1). the stimulated release of noradrenaline from the in situ perfused guinea-pig heart and (2). its presynaptic modulation by the muscarinic agonist carbachol. The release of endogenous noradrenaline from efferent cardiac sympathetic nerve endings was induced by electrical stimulation of the left stellate ganglion (1 min, 5 V, 12 Hz) and quantified in the coronary venous effluent by high-performance liquid chromatography. Under control conditions, two consecutive electrical stimulations (S1, S2) elicited a similar noradrenaline overflow (S2/S1: 0.98 plus minus 0.05). After 10 min of global myocardial ischaemia overflow of endogenous noradrenaline was significantly reduced (S2/S1: 0.18 plus minus 0.03; P< 0.05). When studied separately, metabolic inhibition, hyperkalaemia (16 mM), and acidosis (pH 6.0) each markedly attenuated stimulated noradrenaline overflow (S2/S1: 0.65 plus minus 0.05, 0.43 plus minus 0.14, and 0.37 plus minus 0.09, respectively; P< 0.05). The muscarinic agonist carbachol (10 microM) inhibited stimulated noradrenaline release under normoxic conditions (S2/S1: 0.41 plus minus 0.07; P< 0.05). However, after 10 min of global myocardial ischaemia the inhibitory effect of carbachol on noradrenaline overflow was completely lost. Single components of ischaemia had a differential effect on presynaptic muscarinic modulation. Whereas hyperkalaemia (8-16 mM) did not affect muscarinic inhibition of noradrenaline release, carbachol lost its inhibitory effect during acidosis and metabolic inhibition. In conclusion, hyperkalaemia, metabolic inhibition, and severe acidosis each contribute to reduced overflow of noradrenaline after 10 min of myocardial ischaemia. However, presynaptic muscarinic inhibition of noradrenaline release was not affected by hyperkalaemia, but was sensitive to metabolic inhibition and low degrees of acidosis.

The role of the L-type Ca(2+) channel in refilling functional intracellular Ca(2+) stores in guinea-pig detrusor smooth muscle

The transient rise of intracellular Ca(2+) in detrusor smooth muscle cells is due to the release of Ca(2+) from intracellular stores. However, it is not known how store refilling is maintained at a constant level to ensure constancy of the contractile response. The aim of these experiments was to characterise the role of L-type Ca(2+) channels in refilling. Experiments used isolated guinea-pig detrusor myocytes and store Ca(2+) content was estimated by measuring the magnitude of change to the intracellular [Ca(2+)] ([Ca(2+)](i)) after application of caffeine or carbachol using epifluorescence microscopy. Membrane potential was controlled when necessary by voltage clamp. After Ca(2+) stores were emptied they refilled with an exponential time course, with a time constant of 88 s. The value of the time constant was similar to that of the undershoot of [Ca(2+)](i) following store Ca(2+) release. The degree of store filling was enhanced by maintained depolarisation, or by transient depolarising pulses, and attenuated by L-type Ca(2+) channel antagonists. Inhibition of the sarcoplasmic reticular Ca(2+)-ATPase prevented refilling. Reduction of the resting [Ca(2+)](i) was accompanied by membrane depolarisation; under voltage clamp reduction of [Ca(2+)](i) decreased the number and magnitude of spontaneous transient outward currents. Ca(2+) release from intracellular stores, elicited by caffeine or carbachol, is independent of membrane potential under physiological conditions. However, store refilling occurs via Ca(2+) influx through L-type Ca(2+) channels. Ca(2+) influx is regulated by a feedback mechanism whereby a fall of [Ca(2+)](i) reduces the activity of Ca(2+)-activated K(+) channels, causing cell depolarisation and an enhancement of L-type Ca(2+) channel conductance.

The electrophysiological properties of cultured and freshly isolated detrusor smooth muscle cells

PURPOSE

We generated and characterized a convenient isolated cell model of human detrusor smooth muscle to understand mechanisms that may underlie detrusor instability and provide a suitable model to test potentially useful drugs.

MATERIALS AND METHODS

The electrophysiological properties of freshly isolated detrusor smooth muscle cells from human and guinea pig biopsies were compared with those undergoing cell culture to document in detail the changes that occur during primary culture and subsequent passages as well as the differences in the 2 species.

RESULTS

Resting electrical characteristics were changed in the cultured cells. Membrane potential was less negative (guinea pig -59 versus -42 mV.) and membrane resistance was less (138 versus 124.5 Omegacm.(2)). Regenerative action potentials were recorded in cultured and freshly isolated cells. In guinea pig cells the overall duration and initial rate of depolarization (upstroke) was slower in cultured than in freshly isolated cells, indicative of a decreased magnitude of ionic current in cultured cells. Human cells had a similar prolongation in culture but no decrease in the upstroke rate. Experiments with selective blockers indicated that depolarization is due to influx through L-type Ca2+ channels and repolarization occurred via Ca2+ dependent K+ channels in freshly isolated and cultured cells. No further changes to properties were observed in cells passaged up to 3 times from primary cultured cells.

CONCLUSIONS

Cell culture qualitatively preserves the electrophysiological properties of detrusor smooth muscle cells, although there is some decrease in channel density.

Effect of a decrease in pH on responses mediated by P2 receptors in the rat mesenteric arterial bed

The present study investigated the effect of acidosis (reduction in pH of the Krebs' solution from 7.4 to 6.9) on responses to vasoconstrictors and vasodilators, with a focus on purines, in the rat isolated perfused mesenteric arterial bed. alpha,beta-Methylene ATP (alpha,beta-meATP) (10 microM), a selective P2X receptor agonist, elicited a desensitizing vasocontraction, which was not significantly affected by a reduction in pH to 6.9. Contractions to ATP were also not significantly different at pH 6.9 compared to pH 7.4. In contrast, contractile responses to noradrenaline, methoxamine, and vasopressin were greatly attenuated at pH 6.9 (by 48-83%; P<0.01). At raised tone, vasorelaxations to ADP at P2Y receptors, and to calcitonin gene-related peptide (CGRP), were not different at pH 7.4 and pH 6.9. These data indicate that a reduction in pH (to 6.9) differentially affects responses to vasoconstrictors in the rat mesenteric arterial bed. There is no effect on contractions mediated via P2X receptors, but contractions to noradrenaline, methoxamine and vasopressin are greatly attenuated.

The actions of metabolic inhibition on human detrusor smooth muscle contractility from stable and unstable bladders

OBJECTIVES

To determine the important cellular site(s) of action of a brief exposure to NaCN (chosen to reduce mitochondrial respiration and hence mimic cellular hypoxia) on the mechanical properties and regulation of intracellular [Ca2+] in human detrusor smooth muscle. Using muscle samples obtained from patients with stable and unstable bladders, to determine whether the unstable bladder is associated with changes in the functional properties of detrusor muscle under these circumstances. Materials and methods Experiments were conducted in vitro on muscle strips or isolated cells. Isometric tension was recorded in muscle strips during electrical stimulation or exposure to agonists. Intracellular [Ca2+] and [H+] were measured by epifluorescence microscopy, and cell autofluorescence measured as an index of mitochondrial function.

RESULTS

There were no differences in the responses to electrical stimulation and varying concentrations of carbachol in muscle strips from stable and unstable bladders. NaCN (2 mmol/L) reduced the contraction induced by carbachol (10 micromol/L) by a mean (SD) of 43 (16)% and 56 (15)% in the two groups; the reduction in the unstable was significantly less than in the stable group. NaCN similarly reduced the response to 10 mmol/L caffeine, but had no effect on the KCl-induced contraction. NaCN significantly increased the resting sarcoplasmic [Ca2+] and attenuated the calcium transients evoked by carbachol and caffeine, but again had no effect on the KCl-induced transient. The reduction of the carbachol calcium transient was also less in cells from unstable bladders than in those from stable bladders. There was no effect of NaCN on intracellular pH, except for a brief, transient alkalosis.

CONCLUSIONS

NaCN reduces both the contraction and Ca-transient to carbachol by reducing Ca2+ accumulation by intracellular stores, because the carbachol- and caffeine-evoked responses were similar. Any effect on transmembrane Ca2+ flux was minimal because there was no effect on KCl-induced responses. The greater resilience of tissue from unstable bladders to acute cellular hypoxia may reflect some adaptation acquired in vivo.

Electrophysiological properties of the bladder

The electrophysiological properties of detrusor smooth muscle are described, in particular with regard to their influence on the contractile properties of the tissue. The Ca2+ and K+ channel activities are most important in generating action potentials, but the role of several other ionic currents is described, including Cl-, Ca2+-activated, stretch-activated and ligand-gated channels. The variable appearance and functions of different ionic currents in disease states is discussed, as well as the question of whether electrical activity can transmit between adjacent smooth muscle cells. In addition, the precise role that electrophysiological phenomena play in the regulation of the contractile state of the smooth muscle cells, as well as the generation of bladder electromyograms, is discussed.

The effects of extracellular and intracellular pH on intracellular Ca2+ regulation in guinea-pig detrusor smooth muscle

1. Intracellular pH (pHi) and intracellular [Ca2+] ([Ca2+]i) were measured during changes to superfusate PCO2 and/or [NaHCO3]. Changes to superfusate PCO2 produced sustained changes to pHi and [Ca2+]i, while changes to [NaHCO3] altered only extracellular pH (pHo). 2. Carbachol or caffeine induced a transient rise of [Ca2+]i due to Ca2+ release from an intracellular store. This Ca2+ transient was reduced by extracellular acidosis, but increased by intracellular acidosis. Alkalosis in either compartment produced opposite effects to acidosis. Changes to the Ca2+ transient mirrored those to phasic tension previously reported in this preparation. 3. A raised superfusate [K+] also induced a Ca2+ transient, due to transmembrane influx of Ca2+. This transient was depressed by extracellular acidosis, but unaffected by changes to pHi. The L-type Ca2+ current was similarly affected by changes to pHo, but not by alteration of pHi. 4. The results suggest that extracellular acidosis depresses the Ca2+ transient by reducing transmembrane influx through the L-type Ca2+ channel. The increase in the carbachol- and caffeine-induced Ca2+ transients by intracellular acidosis is due to enhancement of Ca2+ uptake into intracellular stores as a result of a raised resting [Ca2+]i.

A myogenic basis for the overactive bladder

OBJECTIVES

This article summarizes evidence supporting the conclusion that the spontaneous rises in pressure that occur in the overactive bladder, particularly in detrusor instability (DI), regardless of etiology, are myogenic.

METHODS

The evidence quoted has been obtained by several groups of investigators and includes electrophysiologic studies of detrusor myocytes, tension studies of strips of smooth muscle, in vivo experiments on animal models, and light and electron microscopic studies of the structure of the bladder wall.

RESULTS

The results of these studies demonstrate changes in the properties, structure, and innervation of the detrusor. These changes are consistent with the hypothesis that partial denervation of the detrusor may be responsible for altering the properties of the smooth muscle, leading to increased excitability and increased ability of activity to spread between cells, resulting in coordinated myogenic contractions of the whole detrusor.

CONCLUSIONS

It is suggested that alterations in the properties of the detrusor myocytes are a necessary prerequisite for the production of the unstable pressure rises seen in DI of any origin.

External alkalinization decreases intracellular Ca++ and spontaneous contractions in pregnant rat myometrium

OBJECTIVES

As plasma pH rises during pregnancy, the effect of raising external pH on spontaneous contractions in pregnant rat myometrium was investigated to test the hypothesis that elevated external pH depresses contraction.

STUDY DESIGN

Strips of longitudinal myometrium were loaded with SNARF (seminaphthorhodafluor) or Indo-1 for simultaneous intracellular pH or Ca++ and force measurements. Results were obtained from a minimum of five animals in each group, and significant differences were tested for by paired Student t tests.

RESULTS

Raising the external pH significantly reduced spontaneous force and calcium transient in the pregnant uterus. Raising the external pH led to a slow rise in intracellular pH, but this could not account for the functional effect. K+ rubidium 86-labeled efflux rates were unaffected by external pH, suggesting no hyperpolarization. The Ca++ channel agonist Bay K8644 (5 mumol/L) restored contractions abolished by raised external pH.

CONCLUSIONS

Raised external pH reduces spontaneous contractions in the pregnant rat uterus, probably by an external effect on Ca++ entry. This effect may contribute to uterine quiescence before term.

Smooth muscle of the bladder in the normal and the diseased state: pathophysiology, diagnosis and treatment

The smooth muscle of the normal bladder wall must have some specific properties. It must be very compliant and able to reorganise itself during filling and emptying to accommodate the change in volume without generating any intravesical pressure, but whilst maintaining the normal shape of the bladder. It must be capable of synchronous activation to generate intravesical pressure at any length to allow voiding. The cells achieve this through spontaneous electrical activity combined with poor electrical coupling between cells, and a dense excitatory innervation. In the diseased state, alterations of the smooth muscle may lead to failure to store or failure to empty properly. The diseased states discussed are bladder instability and diabetic neuropathy. Bladder instability is characterised urodynamically by uninhibitable rises in pressure during filling, and is seen idiopathically and in association with bladder outflow obstruction and neuropathy. In diabetic neuropathy, many of the smooth muscle changes are a consequence of diuresis, but there is evidence for alterations in the sensory arm of the micturition reflex. In the unstable bladder, additional alterations of the smooth muscle are seen, which are probably caused by the patchy denervation that occurs. The causes of this denervation are not fully established. Nonsurgical treatment of instability is not yet satisfactory; neuromodulation has some promise, but is expensive, and the mechanisms poorly understood. Pharmacological treatment is largely through muscarinic receptor blockade. Drugs to reduce the excitability of the smooth muscle are being sought, since they may represent a better pharmacological option.

An investigation into the mechanism whereby pH affects tension in guinea-pig ureteric smooth muscle

1. We have altered intracellular (pHi) and extracellular pH (pHo) in the smooth muscle of guinea-pig ureter and determined the effects on evoked phasic contractions. In order to investigate the mechanisms underlying the effects of pH alteration, intracellular Ca2+ ([Ca2+]i), pHi, electrical activity and force were measured. 2. Intracellular acidification, produced by the weak acid butyrate, application of CO2 at constant pHo or removal of weak bases, greatly increased phasic contractions. Alkalinization with weak bases or by removal of CO2 inhibited contractions. The results were similar whether Hepes or CO2-HCO3-buffered the solutions. 3. Phasic contractions were preceded by intracellular Ca2+ transients in the ureter. Acidification of the cytoplasm led to an increase in the amplitude of the Ca2+ transient, and alkalinization decreased its magnitude. 4. In the ureter the action potential leads to Ca2+ influx, therefore electrophysiological recordings of its configuration were made during alteration of pHi. Acidification led to the action potential duration and amplitude being increased, whereas alkalinization shortened the action potential and reduced its amplitude. 5. As the effects of acidification on the action potential resembled the effects of blocking of K+ channels, we investigated whether pHi alteration was able to alter tension when K+ channels were blocked by tetraethylammonium. Acidification was unable to potentiate force under these conditions nor did alkalinization decrease force. 6. External pH over the range 6.8-8.0 had little or no effect on pHi, phasic contractions and [Ca2+]i. Tonic contractions were enhanced, however, when pHo was increased. 7. These data suggest that pHi alteration in the guinea-pig ureter modulates the action potential, probably by alteration of K+ currents. Subsequent changes in [Ca2+]i and contraction then occur. A potentiating effect of acidic pH on force is not common in muscle, but may be a characteristic of the smooth muscle of the urinary tract. Changes of pHo had little effect on phasic force or pHi, but modulated tonic contractions. The possible physiological significance of these results is discussed.

Changes of pH affect calcium currents but not outward potassium currents in rat myometrial cells

Spontaneous contraction of uterine smooth muscle is enhanced by alkalinization and depressed by acidification. We have investigated the ionic currents responsible for this in single myometrial cells. Intracellular acidification (20 mM butyrate) at constant external pH depressed the magnitude of the calcium current to 58+/-6% of control, but had little effect on outward currents. Similar but slower effects were also observed when the extracellular pH was lowered to 6.9 (56+/-9% of control). Correspondingly, when the intracellular or extracellular pH was elevated (20 mM NH4Cl or pH 7.9 respectively) the calcium current magnitude increased (165+/-15% in NH4Cl; 136+/-2% at pH 7.9) and there was, again, no effect on the outward currents. These observations are consistent with the effects of pH on spontaneous contractile activity being due to an effect on the membrane calcium current.