Pig bladder

Abstract: Objective To investigate the effect of partial bladder outlet obstruction on detrusor blood flow and oxygen tension (PdetO2) in female pigs Materials and methods Detrusor-layer oxygen tension and blood flow were measured using oxygen-sensitive electrode and radiolabelled microsphere techniques in five female Large White pigs with a partial urethral obstruction and in five sham-operated controls The effects of chronic outlet obstruction on bladder weight, and cholinergic nerve density and distribution, are also described Results In the obstructed bladders, blood flow and oxygen tension were, respectively, 549% and 743% of control values at low bladder volume, and 475% and 425% at cystometric capacity Detrusor blood flow declined by 278% and 375% in the control and obstructed bladders, respectively, as a result of bladder filling, whilst PdetO2 did not decrease in the controls, but fell by 427% in the obstructed bladders Bladder weight increased whilst cholinergic nerve density decreased in the obstructed animals Conclusion In pigs with chronic bladder outlet obstruction, blood flow and oxygen tension in the detrusor layer were lower than in control animals In addition, increasing detrusor pressure during filling caused significantly greater decreases in blood flow and oxygen tension in the obstructed than in the control bladders

Abstract: 1. The effects of alpha,beta-methylene ATP (alpha,beta-MeATP) on membrane properties and excitatory junction potentials (EJPs) were examined in smooth muscle cells of the guinea-pig, rabbit and pig bladder. 2. Intracellular recording with microelectrodes was used to record membrane electrical activity from the guinea-pig bladder. ATP (10(-3) M) produced a rapid, large depolarization with a marked increase in spike frequency, while carbachol (10(-4) M) or acetylcholine (ACh; 10(-4) M) produced only a small or no depolarization with a smaller increase in spike frequency. alpha,beta-MeATP produced a similar response to that of ATP but at a much lower concentration (5 x 10(-6) M), and the response was transient even in the continuous presence of this agent. 3. Changes in the membrane potential and conductance elicited by alpha,beta-MeATP were also measured with the double sucrose-gap method. alpha,beta-MeATP (5 x 10(-6) M) depolarized the membrane and increased the membrane conductance in all three species, but both parameters returned to control values during continuous exposure to this agent. 4. Intracellular recording with microelectrodes showed that in the guinea-pig bladder treatment with alpha,beta-MeATP abolished the response to ATP, while the response to ACh was unchanged. 5. With the double sucrose-gap method, EJPs were elicited by transmural nerve stimulation of strips of the guinea-pig, rabbit and pig bladder and had spikes superimposed, leading to contractions. Desensitization of P2-purinoceptors by alpha,beta-MeATP (3-5 x 10(-6) M) abolished the EJPs and spikes, and reduced the contraction. Atropine (10(-6) M) alone did not alter the EJPs but reduced the contraction. Combined application of both agents abolished the contraction. 6. It is concluded that in the guinea-pig, rabbit and pig bladder ATP is an excitatory transmitter with ACh and EJPs are mediated by ATP.

Abstract: The electrophysiological properties of detrusor smooth muscles have been studied almost exclusively in small mammals and the relevance of the information to the human bladder has been questioned. In the present study, electrical properties of detrusor smooth muscles of the pig and human were investigated using intracellular recording techniques. Bladder smooth muscles of the pig and human exhibited nifedipine (10 μM)-sensitive spontaneous action potentials, and their frequency was highly sensitive to membrane polarization. During bursts of action potentials, each action potential was followed by a fast after-hyperpolarization (fast AHP). Charybdotoxin (CTX, 50 nM) increased the amplitude and duration of action potentials but failed to inhibit the fast AHPs, while apamin (0.1 μM) blocked the fast AHPs and induced action potential complexes, which were followed by slow AHPs. 4-Aminopyridine (4-AP, 1 mM) suppressed the slow AHP and increased action potential frequency. In the human bladder, transmural stimuli initiated inhibitory junction potential-like hyperpolarizations, which were followed by action potential discharges. The hyperpolarizations were blocked by atropine (1 μM) and by apamin (0.1 μM) but not by CTX (50 nM). In the pig bladder, transmural stimuli evoked excitatory junction potentials (EJPs), which triggered action potentials. After desensitizing P2x receptors with α,β methylene-ATP (10 μM), nerve-evoked responses were similar to those of human bladder. These results indicate that detrusor smooth muscles of the pig share many features of electrical properties with those of the human. In addition to large conductance (BK) and small conductance (SK) Ca2+-activated K+ channels, voltage-dependent K+ (VK) channels may play an important role in the regulation of electrical activity of detrusor smooth muscles. British Journal of Pharmacology (2003) 140, 146–158. doi:10.1038/sj.bjp.0705319

Abstract: A hallmark for unstable bladder contractions is hyperexcitability and changes in the nature of spontaneous phasic activity of the bladder smooth muscle. In this study, we have characterized the spontaneous activity of the urinary bladder smooth muscle from the pig, a widely used model for studying human bladder function. Our studies demonstrate that phasic activity of the pig detrusor is myogenic and is influenced by the presence of urothelium. Denuded strips exhibit robust spontaneous activity measured as mean area under the contraction curve (AUC=188.9+/-15.63 mNs) compared to intact strips (AUC=7.3+/-1.94 mNs). Spontaneous phasic activity, particularly the amplitude, is dependent on both calcium entry through voltage-dependent calcium channels and release from ryanodine receptors as shown by inhibition of spontaneous activity by nifedipine and ryanodine respectively. Inhibition of BK(Ca) channels by iberiotoxin (100 nM) resulted in an increase in contraction amplitude (89.1+/-20.4%) and frequency (92.5+/-31.0%). The SK(Ca) channel blocker apamin (100 nM) also increased contraction amplitude (69.1+/-24.3%) and frequency (53.5+/-13.6%) demonstrating that these mechanisms are critical to the regulation of phasic spontaneous activity. Inhibition of K(ATP) channels by glyburide (10 microM) did not significantly alter myogenic contractions (AUC=18.5+/-12.3%). However, K(ATP) channel openers (KCOs) showed an exquisite sensitivity for suppression of spontaneous myogenic activity. KCOs were generally 15 fold more potent in suppressing spontaneous activity compared to contractions evoked by electrical field-stimulation. These studies suggest that potassium channel modulation, particularly K(ATP) channels, may offer a unique mechanism for controlling spontaneous myogenic activity especially those associated with the hyperexcitability occurring in unstable bladders.