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 Ca2+ imaging techniques. The TRPV4 agonist 4α-phorbol-12,13 didecanoate (4α-PDD; 1–5 μM) and the TRPA1/TRPM8 agonist icilin (50–100 μM) elicited transient currents in a high percentage of cells (>70%). 4α-PDD responses were suppressed by the TRPV4 antagonist HC-010961 (10 μM). The TRPV1 agonist capsaicin (1–100 μM) and the TRPA1/TRPM8 agonist menthol (5–200 μM) elicited transient currents in a moderate percentage of cells (∼25%). All of these agonists increased intracellular calcium concentration ([Ca2+]i). Most cells responded to more than one TRP agonist (e.g., capsaicin and 4α-PDD), indicating coexpression of different TRP channels. In the presence of the TRPV1 antagonist capsazepine (10 μM), changes in pH induced by HCl elicited ionic currents (pH 5.5) and increased [Ca2+]i (pH 6.5) in ∼50% of cells. Changes in pH using acetic acid (pH 5.5) elicited biphasic-like currents. Responses induced by acid were sensitive to amiloride (10 μM). In summary, urothelial cells express multiple TRP and ASIC channels, whose activation elicits ionic currents and Ca2+ 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.