Role of the T-type Ca2+ current on the contractile performance of guinea pig detrusor smooth muscle

AIMS: The importance of the T-type Ca(2+) current in determining detrusor contractile function was investigated by using guinea pig muscle in vitro. METHODS: NiCl(2) (200 microM) was used to block selectively the T-type Ca(2+) current, and 20 microM verapamil was used to block the L-type Ca(2+) current in this tissue. The selectivity of these agents at such concentrations has been previously demonstrated. RESULTS: In normal extracellular solution (4 mM KCl) 200 microM NiCl(2) and 20 microM verapamil reduced electrically stimulated contractions by 17 +/- 6% and 65 +/- 10%, respectively. At high concentrations of the two agents, the contraction was completely abolished by NiCl(2) but by only 74 +/- 18% in the case of verapamil; this finding suggests that NiCl(2) has additional negative inotropic actions at higher concentrations. Carbachol and KCl contractures were attenuated to a similar extent to that of electrically stimulated contractions by NiCl(2) and verapamil, which suggests that they act on the muscle rather than the motor nerve. The dependence of the membrane potential on the relative ability of NiCl(2) and verapamil to attenuate the contraction was tested by varying the extracellular [KCl], [KCl](o). Varying [KCl](o) between 2 and 10 mM depolarised detrusor myocytes from (-65.1 +/- 4.7 mV to -42.7 +/- 4.0 mV (a slope of 32 mV per 10-fold change of [KCl](o)). In low [KCl](o),blockade by NiCl(2) was more effective and that of verapamil less effective; at high [KCl](o), the reverse potency was recorded. CONCLUSIONS: The data are consistent with the hypothesis that Ca(2+) influx through both T-type and L-type Ca(2+) channels determines the contractile status of detrusor smooth muscle and that T-type channel activity is more important at membrane potentials near the resting level. A significant role for T-type channel activity in the resting state was evident in that spontaneous contractions were attenuated to a greater extent than evoked contractions.     

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.     

Voiding urgency and detrusor contractility in women with overactive bladders.

AIMS: To check whether the contractility of overactive bladders would be affected by voiding urgency. METHODS: We urodynamically studied 100 women: 20 normal controls (group 1), 60 patients with idiopathic detrusor overactivity (DO), and 20 with neurogenic DO from intracerebral lesions. The idiopathic DO groups 2A (n = 20), 2B (n = 20), and 3 (n = 20) had moderate, severe, and no voiding urgency, respectively. The neurogenic DO group 4 had severe urgency. The delay time of urgent void at cystometry (2 minutes or more or, respectively, less than 2 minutes) defined moderate or severe urgency. Detrusor contractility was defined by the maximum bladder external voiding power (WF(max)). RESULTS: WF(max) was higher in the idiopathic DO patients than in the controls, had the highest values in group 2B, and did not differ significantly between groups 1-4 and 2A-3. CONCLUSIONS: We inferred from our data that idiopathic DO suggests a facilitation of voiding contractions and that such facilitation might be centrally amplified by severe urgency. This amplifying effect would probably be impaired in cases of neurogenic DO from intracerebral lesions.     

Inward calcium currents in cultured and freshly isolated detrusor muscle cells: evidence of a T-type calcium current

PURPOSE: We carefully examined the possible routes of Ca2+ influx, and determined whether cultured cells retain Ca2+ channels and whether the culturing process changes their properties. MATERIALS AND METHODS: Inward currents were measured under voltage clamp in freshly isolated cells and myocytes from confluent cell cultures of detrusor smooth muscle. RESULTS: In guinea pig and human cells mean peak inward current density plus or minus standard deviation decreased significantly in cell culture (2.0 +/- 0.9 versus 4.5 +/- 2.2 pA.pF.(-1)) but there was no species variation. In primary cultured and passaged guinea pig cells an inward current was identified as L-type Ca2+ current. In freshly isolated cells another component to the inward current was identified that was insensitive to 20 micromol. l(-1) verapamil and 20 to 50 micromol. l(-1) cadmium chloride but abolished by 100 micromol. l(-1) nickel chloride and identified as T-type Ca2+ current. In addition, total inward current was greater at a holding potential of -100 than -40 mV., also indicating a component of current activated at negative voltage. Steady state activation and inactivation curves of the net inward current were also compatible with a single component in cultured cells but a dual component in freshly isolated cells. The action potential was completely abolished in cultured cells by L-type Ca2+ channel blockers but incompletely so in freshly isolated cells. Outward current depended strongly on previous inward current, suggesting a predominant Ca2+ dependent outward current. CONCLUSIONS: In freshly isolated guinea pig cells T and L-type Ca2+ current is present but T-type current is absent in confluent cultures.     

Urgency of micturition and detrusor contractility in men with prostatic obstruction and overactive bladders

AIMS: In men with prostatic obstruction and detrusor overactivity (DO), to ascertain whether urgency of micturition affects bladder contractility. MATERIALS AND METHODS: We urodynamically assessed five groups of 20 men each who had bladder outflow obstruction (BOO) from benign prostatic enlargement-Groups 1 (with no DO and no urgency), 2 (with DO and no urgency), 3A (with DO and moderate urgency), 3B (with DO and severe urgency), and 4 (with DO, severe urgency and chronic ischemic cerebral lesions). Urgency was graded as moderate or severe by the ability to avert an urgent void at cystometry for > or =2 or <2 min, respectively. BOO was assessed by the "Abrams-Griffiths number" (AG) and bladder contractility by the parameters PIP and WF(max). RESULTS: AG did not differ significantly in Groups 2, 3A, and 3B, proved higher in such groups than in Group 1, and was nearly the same in Groups 1 and 4. PIP and WF(max) were significantly higher in Groups 2, 3A, and 3B than in Groups 1 and 4, had the highest levels in Group 3B, and did not differ significantly in Groups 1-4 and 2-3A. CONCLUSIONS: In DO patients with prostatic obstruction there seems to be a DO-related facilitation of bladder contractility. In the same patients, severe urgency of micturition might over-amplify (i.e., enhance a DO-related facilitation of) bladder contractility, provided there are no neurogenic (chronic ischemic cerebral) lesions.     

A description of Ca2+ channels in human detrusor smooth muscle

OBJECTIVE: To characterize the Ca2+ channels in human detrusor smooth muscle and to investigate their contribution to spontaneous electrical activity. MATERIALS AND METHODS: Isolated human detrusor smooth muscle myocytes were used to measure ionic currents under voltage-clamp or membrane potential under current-clamp. Membrane potential oscillations were analysed in terms of oscillation frequency and amplitude using fast Fourier transforms. RESULTS: Under voltage-clamp an inward current dependent on extracellular Ca2+ was recorded using Cs+-filled patch electrodes. The current could be separated into two components on the basis of their sensitivity to Ni2+, verapamil or nicardipine, and their dependence on holding and clamp potential. A Ni2+-sensitive component activated over a relatively negative range of potentials (-60 to -20 mV) comprised about a third of the total current and was designated a T-type Ca2+ current. A verapamil/nicardipine-sensitive component, activated at more positive potentials, was designated an l-type Ca2+ current. Using K+-based filling solutions spontaneous transient outward currents were recorded that had the characteristics of current flow through BK channels. Membrane potential oscillations, under current-clamp increased in frequency but not amplitude as the mean membrane potential was made less negative. The voltage-dependence of oscillation frequency was similar to that of the l-type, but not T-type, Ca2+ current activation curve. Furthermore oscillation frequency was slowed by verapamil but not Ni2+. CONCLUSION: The study showed, for the first time, the presence of both T- and L-type Ca2+ channels in human detrusor smooth muscle; we propose a role for these channels in spontaneous activity. The results suggest that the L-type Ca2+ current can control membrane potential oscillation frequency. The significance of this finding for spontaneous contractions is discussed.     

异丙酚对人心房肌细胞瞬时外向整流钾电流的影响

目的 探讨异丙酚对人心房肌细胞瞬时外向整流钾电流(I_(to))的影响.方法 体外循环下行冠状动脉旁路移植术患者,术中于上腔静脉插管前取下右心耳组织,采用急性两步酶解法消化分离成单个心房肌细胞,室温下进行膜片钳全细胞模式记录I_(to).记录不同浓度(25、50、100、150、200 靘ol/L)异丙酚在+50 mV钳制电压下I_(to)的变化,并记录50μmol/L异丙酚对I_(to)激活、失活、失活后再激活动力学的影响.结果 与给药前相比,50、100、150、200 μmol/L异丙酚呈浓度依赖性地抑制I_(to)峰电流密度(P<0.05).给药前、后半数激活电压和斜率因子、半数失活电压和斜率因子、时间常数比较差异无统计学意义(P>0.05).结论 异丙酚可呈浓度依赖性地抑制人心房肌细胞I_(to),产生负性肌力作用,可能是其抗心律失常作用的重要机制之一.     

The effects of halothane, isoflurane, and sevoflurane on Ca2+ current and transient outward K+ current in subendocardial and subepicardial myocytes from the rat left ventricle

Halothane, isoflurane, and sevoflurane abbreviate ventricular action potential duration (APD), and for halothane this effect is greater in the subendocardium than in the subepicardium. In this study we investigated mechanisms underlying the regional effects of these anesthetics on APD. The effect of 0.6 mM halothane, isoflurane, and sevoflurane on the action potential, L-type Ca(2+) current, transient outward K(+) current (I(to)), and steady-state current was recorded in rat left ventricular subendocardial and subepicardial myocytes. Halothane and isoflurane (but not sevoflurane) reduced APD significantly (P < 0.05), more in subendocardial than subepicardial myocytes. Peak L-type Ca(2+) current did not differ between regions and, compared with control, was reduced significantly in both regions by 40% (P < 0.001), 20% (P < 0.001), and 12% (P < 0.01) by halothane, isoflurane, and sevoflurane, respectively. I(to) was greater in subepicardial (3.95 +/- 0.29 nA) than subendocardial (1.12 +/- 0.05 nA) myocytes. In subepicardial myocytes, peak I(to) was reduced significantly by halothane (P < 0.01) and isoflurane (P < 0.05) (by 8% and 7%, respectively) but was unaffected by sevoflurane. No significant reduction of I(to) was observed in subendocardial myocytes with the three anesthetics. The steady-state current was increased significantly (P < 0.05), but the extent of this increase did not differ between the two regions or among the three anesthetics. Therefore, greater inhibition of I(to) in subepicardial than subendocardial myocytes by halothane and isoflurane could underlie their transmural effects on APD.     

The action potential and net membrane currents in isolated human detrusor smooth muscle cells.

The basic electrophysiological properties of the human detrusor have been investigated in vitro using isolated single cells obtained by collagenase digestion of bladder biopsy specimens. Recordings were made using the 'whole-cell patch clamp' technique using either a physiological filling solution or one in which cesium was used to block any outward current. Spontaneous and stimulated action potentials have been recorded and we have performed the first voltage clamp analysis of the currents that underlie the action potential in human detrusor. The depolarising phase of the action potential occurs by an inward current of Ca2+ ions which can be shown to be of sufficient magnitude to support the rate of upstroke. Repolarisation occurs due to an outward K+ current that is partially Ca2+ dependent. The techniques described here permit the investigation of the ionic basis for the control of contractility in the human bladder and may permit the characterisation of any underlying abnormality in the overactive detrusor.     

Determination of Ca2+-release from the isolated smooth muscle cells in suspension from the guinea-pig ileum

Collagenase-dispersed cells from the guinea-pig ileum were prepared and Ca2+ release into Ca2+-depleted solution from the isolated single cells obtained by the centrifugation of the dispersed cells on isotonic sucrose solution was determined with a Ca2+-selective electrode. A technique employing an isotonic sucrose solution for washing isolated cells permitted removal of contaminating extracellular fluids and obtaining the isolated cells with minimum loss of cellular Ca2+. The release of Ca2+ from the dispersed cells consisted of at least two phases. The Ca2+ release into an isotonic sucrose-Tris solution (ISTS) was significantly reduced and the early phase of the Ca2+ release disappeared. At 16 degrees C, Ca2+ release depended on the composition of the bathing solution in a Ca2+-free salt solution, the later phase of Ca2+-release was abolished whereas in ISTS both phases disappeared. Furthermore, Ca2+ release was significantly reduced after the treatment of the dispersed cells with disperse (1,500 units/ml) for 10 min. These results show that Ca2+ release into Ca2+-depleted solution from the isolated ileal cells with minimum loss of cellular Ca2+ show a biphasic curve and suggest that Ca2+ sources responsible for these phases may be of distinct origin.     

The effect of Darifenacin on overactive bladders in female and male rabbits

Our current study utilized a model of bladder instability to compare the effectiveness of darifenacin, a selective m₃ muscarinic antagonist, at inhibiting overactive bladder (OAB) dysfunction in both male and female rabbits. Twenty-four male and female NZ white rabbits were used for this experiment. Each rabbit was anesthetized and the carotid artery was cannulated for blood pressure (BP) monitoring and the left femoral artery was cannulated for acetylcholine (Ach) administration. The bladder dome was catheterized for monitoring bladder pressure and for cystometry. A ligature was placed around the urethra just distal to the bladder to induce OAB. After OAB developed, the response to four IV doses of darifenacin (0.003; 0.01; 0.03; 0.09 mg/kg) evaluated for their effects. Darifenacin: (1) was an equally potent inhibitor of the contractile response of both sexes to intra-arterial Ach, (2) had no effects on BP, (3) was a potent inhibitor of the frequency of OAB, but had a significantly less potent effect on the amplitude, and (4) Darifenacin showed a greater potency in the female rabbits than in the males. These studies provide support for the use of darifenacin in the treatment of OAB.     

The association between overactive bladder and diuretic use in the elderly

Several recent population-based studies have provided insight into the clinical importance and impact of overactive bladder (OAB). Although OAB can affect anyone at any age, the prevalence tends to increase with advancing age. Diuretic use is also common among older adults, as the prevalence of clinical conditions such as hypertension and heart failure requiring its use increases markedly with age. By causing increased formation of urine by the kidneys, diuretics increase urinary frequency and may cause urinary urgency and incontinence. This review provides a summary of available data, focusing on the association between OAB and diuretic use in the elderly. Although there is very little research work in this area, available studies have provided insight into the possible contribution of diuretic use to OAB in the elderly. Based on a recent report, OAB symptoms are common among older adults using diuretics, particularly the loop-type, and are associated with poor quality of life. More studies are required to fully understand the association between diuretic use and OAB, particularly its impact on health-related quality of life.