Two Types of Cation Channel Activated by Stimulation of Muscarinic Receptors in Guinea-Pig Urinary Bladder Smooth Muscle

Masayuki Yamamoto, Toshihiro Unno, Hayato Matsuyama, Masanobu Kohda, Noriyuki Masuda, Masakazu Nishimura, Toshiaki Ishii, Seiichi Komori
2008 Journal of Pharmacological Sciences  
The present study, aiming to elucidate ion channel mechanisms underlying muscarinic receptor-induced depolarization, has characterized membrane currents induced by carbachol in single guinea-pig urinary bladder myocytes. Application of carbachol to cells that were voltageclamped at −50 mV produced an atropine-sensitive, biphasic inward current consisting of an initial peak followed by a smaller sustained phase. Replacing the extracellular Na + and intracellular Cl − with impermeable tris + and
more » ... rmeable tris + and glutamate − , respectively, demonstrated that the biphasic current is entirely composed of cation currents. Its initial peak phase was abolished by buffering intracellular Ca 2+ to a constant level of 100 nM or depleting intracellular Ca 2+ stores, and it was mimicked by the Ca 2+ releaser caffeine. Ca 2+ entry evoked by voltage steps in the sustained phase induced no noticeable change, indicating that this phase of cation current is insensitive to a rise of [Ca 2+ ] i . These results demonstrate that muscarinic receptor stimulation invokes the openings of two types of cation channel, a Ca 2+ -activated and a receptor-operated type; the former channels are gated by a rise in [Ca 2+ ] i upon intracellular Ca 2+ release, and the latter are gated through other muscarinic receptor-coupled signal transduction mechanisms.
doi:10.1254/jphs.08138fp pmid:18987432 fatcat:shqtqqlasvfsrnry7zqpksfclm