Mechanisms underlying spontaneous phasic contractions and sympathetic control of smooth muscle in the rat caudal epididymis.

Here we investigate mechanisms underlying spontaneous phasic contractions (SPCs) and sympathetic control of contractility in the rat epididymis, a long tubular duct involved in transportation and maturation of sperm. Longitudinal contractions of short segments (~ 1.5 mm) of rat proximal and distal caudal epididymal duct were measured + / - nerve stimulation. The extent of sympathetic innervation of these duct regions was determined by immunohistochemistry. Proximal caudal duct segments (150-300 µm dia.) exhibited SPCs, while distal segments (350-500 µm) were quiescent in ~ 80% of preparations. SPC amplitude and frequency were reduced by the L-type voltage-dependent Ca2+ channel (LVDCC) blocker nifedipine (1 µM), with the T-type voltage-dependent Ca2+ channel (TVDCC) blocker ML218 (1 µM) specifically decreasing SPC frequency. SPCs were inhibited upon blockade of the SR/ER Ca2+-ATPase (CPA 10 µM). SPCs were also inhibited by caffeine (1 µM), 2-APB (100 µM), niflumic acid (100 µM), or by lowering extracellular [Cl-] from 134.4 to 12.4 mM but not by ryanodine (25 µM) or tetracaine (100 µM). Electrical field stimulation (EFS) at 2 Hz for 60 s caused a sustained α1-adrenoceptor-sensitive contraction in distal segments and enhanced and/or induced α2-adrenoceptor-sensitive oscillatory phasic contractions in proximal and distal segments, the latter mimicked by application of the α2-adrenoceptor agonist clonidine. We hypothesise that SPCs in the proximal cauda are triggered by pacemaker mechanisms involving rhythmic IP3 receptor-operated SR/ER store Ca2+ release and resultant activation of CaCC with TVDCCs and possibly LVDCCs subserving in this process. Sympathetic nerve-released noradrenaline induces α2-adrenoceptor-mediated phasic contractions in the proximal and distal cauda. These findings provide new pharmacological targets for male infertility and contraception.

Pacemaker Mechanisms Driving Pyeloureteric Peristalsis: Modulatory Role of Interstitial Cells.

The peristaltic pressure waves in the renal pelvis that propel urine expressed by the kidney into the ureter towards the bladder have long been considered to be 'myogenic', being little affected by blockers of nerve conduction or autonomic neurotransmission, but sustained by the intrinsic release of prostaglandins and sensory neurotransmitters. In uni-papilla mammals, the funnel-shaped renal pelvis consists of a lumen-forming urothelium and a stromal layer enveloped by a plexus of 'typical' smooth muscle cells (TSMCs), in multi-papillae kidneys a number of minor and major calyces fuse into a large renal pelvis. Electron microscopic, electrophysiological and Ca2+ imaging studies have established that the pacemaker cells driving pyeloureteric peristalsis are likely to be morphologically distinct 'atypical' smooth muscle cells (ASMCs) that fire Ca2+ transients and spontaneous transient depolarizations (STDs) which trigger propagating nifedipine-sensitive action potentials and Ca2+ waves in the TSMC layer. In uni-calyceal kidneys, ASMCs predominately locate on the serosal surface of the proximal renal pelvis while in multi-papillae kidneys they locate within the sub-urothelial space. 'Fibroblast-like' interstitial cells (ICs) located in the sub-urothelial space or adventitia are a mixed population of cells, having regional and species-dependent expression of various Cl-, K+, Ca2+ and cationic channels. ICs display asynchronous Ca2+ transients that periodically synchronize into bursts that accelerate ASMC Ca2+ transient firing. This review presents current knowledge of the architecture of the proximal renal pelvis, the role Ca2+ plays in renal pelvis peristalsis and the mechanisms by which ICs may sustain/accelerate ASMC pacemaking.

Excitation-Contraction Coupling in Ureteric Smooth Muscle: Mechanisms Driving Ureteric Peristalsis.

The ureter acts as a functional syncytium and is controlled by a propagating plateau-type action potential (AP) which gives rise to a wave of contraction (ureteral peristalsis) via a process called excitation-contraction (E-C)coupling. The second messenger Ca2+ activates Ca2+/calmodulin-dependent myosin light chain kinase-dependent phosphorylation of 20-kDa regulatory light chains of myosin which leads to ureteric contraction. Ca2+ entry from the extracellular space via voltage-gated L-type Ca2+ channels (VGCCs) provides the major source of activator Ca2+, responsible for generation of both the AP and a Ca2+ transient that appears as an intercellular Ca2+ wave. The AP, inward Ca2+ current, Ca2+ transient and twitch contraction are all fully blocked by the selective L-type Ca2+ channel blocker nifedipine. Ca2+ entry via VGCCs, coupled to activation of Ca2+-sensitive K+ (KCa) or Cl- (ClCa) channels, acts as a negative or positive feedback mechanism, respectively, to control excitability and the amplitude and duration of the plateau component of the AP, Ca2+ transient and twitch contraction. The ureter, isolated from the pelvis, is not spontaneously active. However, spontaneous activity can be initiated in the proximal and distal ureter by a variety of biological effectors such as neurotransmitters, paracrine, endocrine and inflammatory factors. Applied agonists depolarise ureteric smooth muscles cells to threshold of AP activation, initiating propagating intercellular AP-mediated Ca2+ waves to produce antegrade and/or retrograde ureteric peristalsis. Several mechanisms have been proposed to describe agonist-induced depolarization of ureteric smooth muscle, which include suppression of K+ channels, stimulation of ClCa current and activation of non-selective cation receptor/store operated channels.

Interstitial cell modulation of pyeloureteric peristalsis in the mouse renal pelvis examined using FIBSEM tomography and calcium indicators.

Typical and atypical smooth muscle cells (TSMCs and ASMCs, respectively) and interstitial cells (ICs) within the pacemaker region of the mouse renal pelvis were examined using focused ion beam scanning electron (FIB SEM) tomography, immunohistochemistry and Ca2+ imaging. Individual cells within 500-900 electron micrograph stacks were volume rendered and associations with their neighbours established. 'Ribbon-shaped', Ano1 Cl- channel immuno-reactive ICs were present in the adventitia and the sub-urothelial space adjacent to the TSMC layer. ICs in the proximal renal pelvis were immuno-reactive to antibodies for CaV3.1 and hyperpolarization-activated cation nucleotide-gated isoform 3 (HCN3) channel sub-units, while basal-epithelial cells (BECs) were intensely immuno-reactive to Kv7.5 channel antibodies. Adventitial to the TSMC layer, ASMCs formed close appositions with TSMCs and ICs. The T-type Ca2+channel blocker, Ni2+ (10-200 µM), reduced the frequency while the L-type Ca2+ channel blocker (1 µM nifedipine) reduced the amplitude of propagating Ca2+ waves and contractions in the TSMC layer. Upon complete suppression of Ca2+ entry through TSMC Ca2+ channels, ASMCs displayed high-frequency (6 min-1) Ca2+ transients, and ICs distributed into two populations of cells firing at 1 and 3 min-1, respectively. IC Ca2+ transients periodically (every 3-5 min-1) summed into bursts which doubled the frequency of ASMC Ca2+ transient firing. Synchronized IC bursting and the acceleration of ASMC firing were inhibited upon blockade of HCN channels with ZD7288 or cell-to-cell coupling with carbenoxolone. While ASMCs appear to be the primary pacemaker driving pyeloureteric peristalsis, it was concluded that sub-urothelial HCN3(+), CaV3.1(+) ICs can accelerate ASMC Ca2+ signalling.

Spontaneous activity in the microvasculature of visceral organs: role of pericytes and voltage-dependent Ca(2+) channels.

The microvasculature plays a primary role in the interchange of substances between tissues and the circulation. In visceral organs that undergo considerable distension upon filling, the microvasculature appears to display intrinsic contractile properties to maintain their flow. Submucosal venules in the bladder or gastrointestinal tract generate rhythmic spontaneous phasic constrictions and associated Ca(2+) transients. These events are initiated within either venular pericytes or smooth muscle cells (SMCs) arising from spontaneous Ca(2+) release from the sarcoplasmic reticulum (SR) and the opening of Ca(2+) -activated chloride channels (CaCCs) that trigger Ca(2+) influx through L-type voltage-dependent Ca(2+) channels (VDCCs). L-type VDCCs also play a critical role in maintaining synchrony within the contractile mural cells. In the stomach myenteric layer, spontaneous Ca(2+) transients originating in capillary pericytes appear to spread to their neighbouring arteriolar SMCs. Capillary Ca(2+) transients primarily rely on SR Ca(2+) release, but also require Ca(2+) influx through T-type VDCCs for their synchrony. The opening of T-type VDCCs also contribute to the propagation of Ca(2+) transients into SMCs. In visceral microvasculature, pericytes act as either spontaneously active contractile machinery of the venules or as pacemaker cells generating synchronous Ca(2+) transients that drive spontaneous contractions in upstream arterioles. Thus pericytes play different roles in different vascular beds in a manner that may well depend on the selective expression of T-type and L-type Ca(2+) channels.

Angiotensin receptor-1A knockout leads to hydronephrosis not associated with a loss of pyeloureteric peristalsis in the mouse renal pelvis.

The action of angiotensin II (AngII) on the Ca(2+) signals driving pyeloureteric peristalsis was investigated using both conventional and angiotensin receptor (ATr) ATr1A and ATr2 knockout ((-/-)) mice. Contractility in the renal pelvis of adult ATr1A(-/-) and ATr2(-/-) mice was compared to their respective wildtype (ATr1A(+/+) and ATr2(+/+)) controls of the same genetic background (FVB/N and C57Bl/6 respectively) using video microscopy. The effects of AngII on the Ca(2+) signals in typical and atypical smooth muscle cells (TSMCs and ASMCs, respectively) within the pelvic wall of conventional mice were recorded using Fluo-4 Ca(2+) imaging. Compared to ATr1A(+/+) , ATr2(+/+) and ATr2(-/-) mice, kidneys of the ATr1A(-/-) mouse were mildly-to-severely hydronephrotic, associated with an enlarged calyx, an atrophic papilla and a hypoplastic renal pelvis. Contraction frequencies in the renal pelvis of moderately hydronephrotic ATr1A(-/-) and unaffected ATr2(-/-) mice were not significantly different from their ATr1A(+/+), ATr2(+/+) controls. No contractions were observed in severely-hydronephrotic ATr1A(-/-) kidneys. AngII increased the spontaneous contraction frequency of the renal pelvis in ATr1A(+/+), ATr2(+/+) and ATr2(-/-) mice, but had little effect on the contractions in the mildly-hydronephrotic ATr1A(-/-) renal pelvis. The ATr1 blocker, candesartan prevented the positive chronotropic effects of AngII. AngII increased the frequency and synchronicity of Ca(2+) transients in both TSMCs and ASMCs. It was concluded that the hydronephrosis observed in ATr1A(-/-) mouse kidneys does not arise from a failure in the development of the essential pacemaker and contractile machinery driving pyeloureteric peristalsis.

Voltage-operated Ca(2) (+) currents and Ca(2) (+) -activated Cl(-) currents in single interstitial cells of the guinea-pig prostate.

OBJECTIVE: To investigate the expression of 'T-type' and 'L-type' voltage-operated Ca(2) (+) channels in single interstitial cells of the guinea-pig prostate. MATERIAL AND METHODS: Whole-cell and perforated patch-clamp techniques were applied to prostatic interstitial cells (PICs) dispersed using collagenase. RESULTS: In contrast to prostatic myocytes, PICs under voltage clamp and filled with K(+) (130 mm) were distinguished by the absence of a voltage-operated transient outward K(+) current or spike discharge upon membrane depolarisation when under current clamp. Depolarisation of Cs(+) -filled PICs evoked an inward current at potentials positive to -60 mV, which peaked in amplitude near 0 mV. This inward current increased when Ba(2+) (5 mm) replaced the external Ca(2) (+) (1.5 mm) and displayed a variable sensitivity to the inhibitory actions of conditioning depolarisations to -40 mV applied before the test depolarisation or to 1 µm nifedipine, the 'L-type' Ca(2) (+) channel blocker. A residual inward current recorded in nifedipine was blocked by 10 µm Ni(2) (+) . Cs(+) -filled PICs also displayed a slowly inactivating outward current that was little affected by nifedipine, reduced by the Cl(-) channel blocker, niflumic acid (10 µm) and blocked by Ba(2) (+) or a conditioning depolarisation. CONCLUSION: PICs express both a small 'T-type' Ca(2) (+) channel current (ICa ) and a large 'L-type' ICa . Ca(2) (+) influx through 'T-type' ICa was an essential trigger for the activation of a Ca(2) (+) -activated Cl(-) -selective current. The dependence of PIC Ca(2) (+) signalling on 'T-type' and 'L-type' ICa is unique compared with other interstitial cells of the urogenital tract and may well be pharmaceutically exploitable.

Effects of imatinib mesylate on the spontaneous activity generated by the guinea-pig prostate.

UNLABELLED: What's known on the subject? and what does the study add?: Several studies have examined the functional role of tyrosine kinase receptors in the generation of spontaneous activity in various segments of the gastrointestinal and urogenital tracts through the application of its inhibitor, imatinib mesylate (Glivec®), but results are fairly inconsistent. This is the first study detailing the effects of imatinib mesylate on the spontaneous activity in the young and ageing prostate gland. As spontaneous electrical activity underlies the spontaneous rhythmic prostatic contractions that occur at rest, elucidating the mechanisms involved in the regulation of the spontaneous electrical activity and the resultant phasic contractions could conceivably lead to the identification of better targets and the development of more specific therapeutic agents to treat prostate conditions. OBJECTIVE: To investigate the effect of imatinib mesylate, a tyrosine kinase receptor inhibitor, in the generation of spontaneous electrical and contractile activity in the young and ageing guinea-pig prostate. MATERIALS AND METHODS: Standard tension and intracellular recording were used to measure spontaneous contractions and slow waves, respectively from the guinea-pig prostate at varying concentrations of imatinib mesylate (1-50 µm). RESULTS: Imatinib mesylate (1-10 µm), did not significantly affect slow waves recorded in the prostate of both age groups but at 50 µm, the amplitude of slow waves from the ageing guinea-pig prostate was significantly reduced (P < 0.05, n = 5). In contrast, the amplitude of contractions across all concentrations in the young guinea-pig prostate was reduced to between 35% and 41% of control, while the frequency was reduced to 15.7% at 1 µm (n = 7), 49.8% at 5 µm (n = 10), 46.2% at 10 µm (n = 7) and 53.1% at 50 µm (n = 5). Similarly, imatinib mesylate attenuated the amplitude and slowed the frequency of contractions in ageing guinea-pigs to 5.15% and 3.3% at 1 µm (n = 6); 21.1% and 20.8% at 5 µm (n = 8); 58.4% and 8.8% at 10 µm (n = 11); 72.7% and 60% at 50 µm (n = 5). CONCLUSIONS: A significant reduction in contractions but persistence of slow waves suggests imatinib mesylate may affect the smooth muscle contractile mechanism. Imatinib mesylate also significantly reduced contractions in the prostates of younger guinea pigs more than older ones, which is consistent with the notion that the younger guinea-pig prostate is more reliant on the tyrosine-dependent pacemaker ability of interstitial cells of Cajal-like prostatic interstitial cells.

Association between congenital defects in papillary outgrowth and functional obstruction in Crim1 mutant mice.

Crim1 hypomorphic (Crim1(KST264/KST264)) mice display progressive renal disease characterized by glomerular defects, leaky peritubular vasculature, and progressive interstitial fibrosis. Here we show that 27% of these mice also present with hydronephrosis, suggesting obstructive nephropathy. Dynamic magnetic resonance imaging using Magnevist showed fast development of hypo-intense signal in the kidneys of Crim1(KST264/KST264) mice, suggesting pooling of filtrate within the renal parenchyma. Rhodamine dextran (10 kDa) clearance was also delayed in Crim1(KST264/KST264) mice. Pyeloureteric peristalsis, while present, was less co-ordinated in Crim1(KST264/KST264) mice. However, isolated renal pelvis preparations suggest normal pelvic smooth muscle contractile responses. An analysis of maturation during the immediate postnatal period [postnatal day (P) 0-15] revealed defects in papillary extension in Crim1({KST264/KST264) mice. While Crim1 expression is weak in pelvic smooth muscle, strong expression is seen in the interstitium and loops of Henle of the extending papilla, commencing at the tip of the P1 papilla and disseminating throughout the papilla by P15. These results, as well as implicating Crim1 in papillary extension and pelvic smooth muscle contractility, highlight the previously unrecognized association between defects in papillary development and progression to chronic kidney disease later in life.

Nitric oxide signaling pathways involved in the inhibition of spontaneous activity in the guinea pig prostate.

PURPOSE: We investigated nitric oxide mediated inhibition of spontaneous activity recorded in young and aging guinea pig prostates. MATERIALS AND METHODS: Conventional intracellular microelectrode and tension recording techniques were used. RESULTS: The nitric oxide donor sodium nitroprusside (10 µM) abolished spontaneous contractions and slow wave activity in 5 young and 5 aging prostates. Upon adding the nitric oxide synthase inhibitor L-NAME (10 µM) the frequency of spontaneous contractile and electrical activity was significantly increased in each age group. This increase was significantly larger in 4 to 8 preparations of younger vs aging prostates (about 40% to 50% vs about 10% to 20%, 2-way ANOVA p<0.01). Other measured parameters, including the duration, amplitude and membrane potential of spontaneous electrical and contractile activity, were not altered from control values. The guanylate cyclase inhibitor ODQ (10 µM) significantly increased the frequency of spontaneous activity by 10% to 30% in 6 young guinea pig prostates (Student paired t test p<0.05). However, it had no effect on aging prostates. The cGMP analogue 8-Br-GMP (1 µM) and the PDE5 inhibitor dipyridamole (1 µM) significantly decreased the frequency of contractile activity by about 70% in 4 to 9 young and older prostates (Student paired t test p<0.05). CONCLUSIONS: The decrease in the response to L-NAME in spontaneous contractile and slow wave activity in aging prostate tissue compared to that in young prostates suggests that with age there is a decrease in nitric oxide production. This may further explain the increase in prostatic smooth muscle tone observed in age related prostate specific conditions, such as benign prostatic hyperplasia.

A targeted NKX2.1 human embryonic stem cell reporter line enables identification of human basal forebrain derivatives.

We have used homologous recombination in human embryonic stem cells (hESCs) to insert sequences encoding green fluorescent protein (GFP) into the NKX2.1 locus, a gene required for normal development of the basal forebrain. Generation of NKX2.1-GFP(+) cells was dependent on the concentration, timing, and duration of retinoic acid treatment during differentiation. NKX2.1-GFP(+) progenitors expressed genes characteristic of the basal forebrain, including SHH, DLX1, LHX6, and OLIG2. Time course analysis revealed that NKX2.1-GFP(+) cells could upregulate FOXG1 expression, implying the existence of a novel pathway for the generation of telencephalic neural derivatives. Further maturation of NKX2.1-GFP(+) cells gave rise to γ-aminobutyric acid-, tyrosine hydroxylase-, and somatostatin-expressing neurons as well as to platelet-derived growth factor receptor α-positive oligodendrocyte precursors. These studies highlight the diversity of cell types that can be generated from human NKX2.1(+) progenitors and demonstrate the utility of NKX2.1(GFP/w) hESCs for investigating human forebrain development and neuronal differentiation.

Spontaneous Ca2+ signaling of interstitial cells in the guinea pig prostate.

PURPOSE: We investigated whether prostate interstitial cells generate spontaneous Ca(2+) oscillation, a proposed mechanism underlying pacemaker potentials to drive spontaneous activity in stromal smooth muscle cells. MATERIALS AND METHODS: Intracellular free Ca(2+) in portions of guinea pig prostate and freshly isolated, single prostate interstitial cells were visualized using fluo-4 Ca(2+) fluorescence. Spontaneous electrical activity was recorded in situ with intracellular microelectrodes. RESULTS: In whole tissue preparations spontaneous Ca(2+) flashes firing synchronously across all smooth muscle cells within the field of view resulted in muscle wall contractions. Nonpropagating Ca(2+) waves were also recorded in individual smooth muscle cells. Nifedipine (Sigma®) (1 µM) largely decreased or abolished these Ca(2+) flashes and suppressed slow wave discharge upon blockade of their superimposed action potentials. Isolated prostate interstitial cells were readily distinguished from smooth muscle cells by their spiky processes and lack of contraction during intracellular Ca(2+) increases. Prostate interstitial cells generated spontaneous Ca(2+) transients in the form of whole cell flashes, intracellular Ca(2+) waves or localized Ca(2+) sparks. All 3 Ca(2+) signals were abolished by nicardipine (1 µM), cyclopiazonic acid (10 µM), caffeine (Sigma) (10 mM) or extracellular Ca(2+) removal. CONCLUSIONS: Prostate interstitial cells generate spontaneous Ca(2+) transients that occur at a frequency comparable to Ca(2+) flashes in situ or slow waves relying on functional internal Ca(2+) stores. However, unlike other interstitial cells in the urinary tract, Ca(2+) influx through L-type Ca(2+) channels is fundamental to Ca(2+) transient firings in prostate interstitial cells. Thus, it is not possible to conclude that prostate interstitial cells are responsible for pacemaker potential generation.

Contractility and pacemaker cells in the prostate gland.

PURPOSE: We focused on the current opinion on mechanisms generating stromal tone in the prostate gland. MATERIALS AND METHODS: We selected the guinea pig as the main species for investigation since its prostate has a high proportion of smooth muscle that undergoes age related changes similar in many respects to that in humans. The main techniques that we used were tension recording and electrophysiology. RESULTS: We previously reported distinct electrical activity and cell types in the prostate, and speculated on their functional roles. We believe that a specialized group of c-kit immunoreactive prostatic interstitial cells that lie between glandular epithelium and smooth muscle stroma have a role similar to that of gastrointestinal interstitial cells of Cajal, generating the pacemaker signal that manifests as slow wave activity and triggers contraction in smooth muscle cells in guinea pig prostates. CONCLUSIONS: Since changes in muscle tone are involved in the etiology of age dependent prostate specific conditions such as benign prostatic hyperplasia, knowledge of the electrical properties of the various prostatic cell types and their interactions with each other, with nerves and with the hormonal environment, and how these factors change with age is of considerable medical importance.

Functions of ICC-like cells in the urinary tract and male genital organs.

Interstitial cells of Cajal (ICC)-like cells (ICC-LCs) have been identified in many regions of the urinary tract and male genital organs by immunohistochemical studies and electron microscopy. ICC-LCs are characterized by their spontaneous electrical and Ca(2+) signalling and the cellular mechanisms of their generation have been extensively investigated. Spontaneous activity in ICC-LCs rises from the release of internally stored Ca(2+) and the opening of Ca(2+)-activated Cl(-) channels to generate spontaneous transient depolarizations (STDs) in a manner not fundamentally dependent on Ca(2+) influx through L-type voltage-dependent Ca(2+) channels. Since urogenital ICC-LCs have been identified by their immunoreactivity to Kit (CD117) antibodies, the often-used specific marker for ICC in the gastrointestinal tract, their functions have been thought likely to be similar. Thus ICC-LCs in the urogenital tract might be expected to act as either electrical pacemaker cells to drive the smooth muscle wall or as intermediaries in neuromuscular transmission. However, present knowledge of the functions of ICC-LCs suggests that their functions are not so predetermined, that their functions may be very region specific, particularly under pathological conditions. In this review, we summarize recent advances in our understanding of the location and function of ICC-LCs in various organs of the urogenital system. We also discuss several unsolved issues regarding the identification, properties and functions of ICC-LCs in various urogenital regions in health and disease.

Role of hyperpolarization-activated cation channels in pyeloureteric peristalsis.

Although it has been recognized for more than 140 years that the pacemaker driving pyeloureteric peristalsis resides within the kidney, the cellular mechanisms underlying this autorhythmicity have been little investigated. The demonstration by Hurtado et al. of a role of hyperpolarization-activated cation channels in the maintenance of coordinated propagating contractions in the mouse renal pelvis raises a number of intriguing possibilities in addition to the provided correlation with 'pacemaker' function as in the heart and neurons.

Spontaneous electrical and Ca2+ signals in the mouse renal pelvis that drive pyeloureteric peristalsis.

1. Peristalsis in the smooth muscle cell (SMC) wall of the pyeloureteric system is unique in physiology in that the primary pacemaker resides in a population of atypical SMCs situated near the border of the renal papilla. 2. Atypical SMCs display high-frequency Ca(2+) transients upon the spontaneous release of Ca(2+) from inositol 1,4,5-trisphosphate (IP(3))-dependent stores that trigger cation-selective spontaneous transient depolarizations (STDs). In the presence of nifedipine, these Ca(2+) transients and STDs seldom propagate > 100 mum. Synchronization of STDs in neighbouring atypical SMCs into an electrical signal that can trigger action potential discharge and contraction in the typical SMC layer involves a coupled oscillator mechanism dependent on Ca(2+) entry through L-type voltage-operated Ca(2+) channels. 3. A population of spindle- or stellate-shaped cells, immunopositive for the tyrosine receptor kinase kit, is sparsely distributed throughout the pyeloureteric system. In addition, Ca(2+) transients and action potentials of long duration occurring at low frequencies have been recorded in a population of fusiform cells, which we have termed interstitial cells of Cajal (ICC)-like cells. 4. The electrical and Ca(2+) signals in ICC-like cells are abolished upon blockade of Ca(2+) release from either IP(3)- or ryanodine-dependent Ca(2+) stores. However, the spontaneous Ca(2+) signals in atypical SMCs or ICC-like cells are little affected in W/W(-v) transgenic mice, which have extensive lesions of their intestinal ICC networks. 5. In summary, we have developed a model of pyeloureteric pacemaking in which atypical SMCs are indeed the primary pacemakers, but the function of ICC-like cells has yet to be determined.

Spontaneous electrical waveforms in aging guinea pig prostates.

PURPOSE: We characterized spontaneous electrical activity in the aging guinea pig prostate. MATERIALS AND METHODS: Membrane potential recordings were made using conventional single microelectrode recording techniques. RESULTS: Three types of spontaneous waveforms were recorded, including spikes, slow waves and spontaneous transient depolarizations. Spikes were classified as hyperactive or active. Active cells showed a mean +/- SEM frequency of 5.06 +/- 0.63 minutes(-1), significantly different from that in hyperactive cells (362.05 +/- 151.82 minutes(-1), p <0.05). After hyperpolarization amplitude was also significantly different in the active and hyperactive groups (17.80 +/- 1.98 vs 9.96 +/- 1.05 mV). Spike activity was abolished by 1 microM nifedipine in 7 preparations (p <0.05). Slow wave activity occurred at a frequency of 5.2 +/- 0.5 minutes(-1). The spike component of slow wave activity was abolished by 1 microM nifedipine, although the depolarizing transient remained unaltered from control values (8.1 +/- 3.1 mV, paired Student's t test p >0.05). Spontaneous transient depolarizations were recorded in the presence of slow waves in 10 preparations and of spikes in 13, and in quiescent cells in 9. Spontaneous transient depolarization frequency was highest in otherwise quiescent cells (24.55 +/- 6.48 minutes(-1)) compared to that in the presence of slow waves or spikes. Adding 1 microM nifedipine in 5 preparations did not significantly affect any measured parameters (p >0.05). Pacemaker potentials were not recorded in the aging prostate. CONCLUSIONS: With increased age there is an increase in spike activity, which could conceivably explain the increased prostatic tone that accompanies aging. Spike activity and the spike component of the slow wave were abolished by nifedipine, suggesting a role for L-type channels. Finally, spontaneous transient depolarizations were unaffected by nifedipine, suggesting that mechanisms other than Ca(2+) entry via L-type channels are responsible for their generation and maintenance.

Pelviureteric peristaltic contractions in diabetic rats.

The effects of strepozotocin (STZ)-induced diabetes on the spontaneous peristaltic contractions in the upper urinary tract (UUT) of the rat were examined by simultaneously recording the tension in the proximal and distal regions of the renal pelvis and the proximal ureter. All regions of the UUT of diabetic rats contracted at a frequency similar to the contraction frequency of age-matched control rats. In contrast, contraction amplitudes in the proximal and distal renal pelvis and ureter of diabetic rats were 36%, 135% and 121% larger than the equivalent contractions recorded in control rats resulting in a significant increases in the motility index (MI amplitude x frequency) in all 3 regions. Capsaicin (10 microM), substance P (SP 2 microM) and neurokinin A (NKA 2 microM) caused a transient increase in MI in both control and STZ-induced diabetic rats. The rise in basal tension in the proximal and distal renal pelvis evoked by capsaicin, SP or NKA was also significantly greater in the diabetic rats when compared with controls. In contrast, human calcitonin-gene related peptide (hCGRP) produced a relatively small transient inhibition of UUT motility which was little affected by STZ treatment. These results suggest that capsaicin predominantly releases tachykinins from intrinsic sensory nerves in both non-diabetic and STZ-induced diabetic rats. We speculate that the supersensitivity of the diabetic UUT to capsaicin, NKA and SP 8-10 weeks after STZ treatment could be arising from an earlier development of sensory neuropathy.

Role of prostatic interstitial cells in prostate motility.

The prostate is a gland whose secretions contribute to the seminal fluids ejaculated upon activation of autonomic sympathetic nerves. In elder males, the prostate undergoes an increase in stroma mass and myogenic tone, leading to benign prostatic hyperplasia that occludes the proximal urethra and the presentation of various lower urinary tract symptoms that decrease their quality of life. This review summarises the role of prostatic interstitial cells (PICs) in the generation of the spontaneous tone in the prostate. It presents current knowledge of the role of Ca2+ plays in PIC pacemaking, as well as the mechanisms by which this spontaneous activity triggers slow wave generation and stromal contraction. PICs display a small T-type Ca2+ current (ICaT) and a large L-type Ca2+ current (ICaL). In contrast to other interstitial cells in the urinary and gastrointestinal tracts, spontaneous Ca2+ signalling in PICs is uniquely dependent on Ca2+ influx through ICaL channels. A model of prostatic pacemaking is presented describing how ICaL can be triggered by an initial membrane depolarization evoked upon the selective opening of Ca2+-activated Cl- channels by Ca2+ flowing only through ICaT channels. The resulting current flow through ICaL results in release of Ca2+ from internal stores and the summation of Cl--selective spontaneous transient depolarizations (STDs) to form pacemaker potentials that propagate passively into the prostatic stroma to evoke regenerative action potentials and excitation-contraction coupling.