Functional TRP and ASIC-like channels in cultured urothelial cells from the rat

Abstract

Transient receptor potential (TRP) and acid-sensing ion channels (ASIC) are molecular detectors of chemical, mechanical, thermal, and nociceptive stimuli in sensory neurons. They have been identified in the urothelium, a tissue considered part of bladder sensory pathways, where they might play a role in bladder function. This study investigated functional properties of TRP and ASIC channels in cultured urothelial cells from the rat using patch-clamp and fura 2 Ca 2ϩ imaging techniques. The TRPV4 agonist 4␣-phorbol-12,13 didecanoate (4␣-PDD; 1-5 M) and the TRPA1/TRPM8 agonist icilin (50 -100 M) elicited transient currents in a high percentage of cells (Ͼ70%). 4␣-PDD responses were suppressed by the TRPV4 antagonist HC-010961 (10 M). The TRPV1 agonist capsaicin (1-100 M) and the TRPA1/TRPM8 agonist menthol (5-200 M) elicited transient currents in a moderate percentage of cells (ϳ25%). All of these agonists increased intracellular calcium concentration ([Ca 2ϩ ]i). Most cells responded to more than one TRP agonist (e.g., capsaicin and 4␣-PDD), indicating coexpression of different TRP channels. In the presence of the TRPV1 antagonist capsazepine (10 M), changes in pH induced by HCl elicited ionic currents (pH 5.5) and increased [Ca 2ϩ ]i (pH 6.5) in ϳ50% of cells. Changes in pH using acetic acid (pH 5.5) elicited biphasic-like currents. Responses induced by acid were sensitive to amiloride (10 M). In summary, urothelial cells express multiple TRP and ASIC channels, whose activation elicits ionic currents and Ca 2ϩ influx. These "neuron-like" properties might be involved in transmitter release, such as ATP, that can act on afferent nerves or smooth muscle to modulate their responses to different stimuli. bladder; fura 2 calcium imaging; patch clamp TRANSIENT RECEPTOR POTENTIAL (TRP) channels are nonselective cation channels that function as sensors for various stimuli, including temperature, mechanical stretch, or chemicals (2, 53). They are highly expressed in primary sensory neurons, where they play a critical role in nociception, mechano-, and thermosensation. In these neurons, distinct sets of TRP channels are coexpressed in different populations of cells. This differential pattern of expression confers functional heterogeneity to primary sensory neurons, and it is the basis for detection of sensory information (8,16,31,32,53). TRPV1 is a capsaicin/heat/pH-sensitive channel (16,17); TRPV4 is an osmotic/temperature/mechanical and shear stress detector (24, 36); TRPM8 is a cold (Ͻ22-26°C)/menthol/icilin-activated channel (38, 41); and TRPA1 is a noxious cold-sensitive channel (Ͻ17°C), also sensitive to cinnamaldehyde, mustard oil, menthol, and icilin (4, 49).Immunohistochemistry and RT-PCR identified several TRP channels including TRPV1, TRPV4, TRPM8, and TRPA1 in the urothelium, a specialized epithelial tissue believed to be involved in the detection of chemical and mechanical information and the generation of sensory input from the bladder to the spinal cord (2, 3, 12, 13, 22-24, 28, 39, 48, 50). Since the di...

Urothelial Signaling

“…TRPV4 was initially described in the urothelium of rodents and humans (146). Coexpression of the two receptors was observed in 20% of rat urothelial cells (167). TRPV4 may also be expressed in bladder afferents; ϳ30% of L6 dorsal root ganglia neurons that project to the urinary bladder coexpressed TRPV1 and TRPV4 (57,66).…”

A method to study bladder urothelial cellular function in situ

“…However, presence of active potassium channels, including Kir2.1 and BK, have been detected in cultured human bladder urothelial cells, with altered function of these channels in interstitial cystitis and overactive bladder [15,16]. The conductance of Kir2.1 is small (~27 pS) [15], whereas conductance of BK is large (~180 pS) [16], so the 22 pS potassium current detected in this study might be Kir2.1. It should be noted that these channel activities in the prior urothelial studies were measured in cultured monolayer of cells from human subjects.…”

The effect of hyperosmolar stimuli and cyclophosphamide on the culture of normal rat urothelial cells in vitro

“…Also, different mechanisms of apoptotic cell removal from the tissue have been described: the cells can be exfoliated into the lumen of an organ; they can be phagocytosed and digested, mostly by macrophages, or even by adjacent cells in tumours [23][24][25][26]. Moreover, Kullmann et al [27] showed that stimulation of different receptors (TRPV1, TRPV4, TRPM8, TRPA1, and ASIC-like channels) in primary urothelial cell culture induces ionic currents and changes in intracellular calcium concentration. It was postulated that TRP channels might be involved in the mechanisms underlying the release of transmitters from the urothelium and might contribute to the putative sensory function of the urothelium, as well as playing a role in homeostatic mechanisms related to cell proliferation and differentiation.…”