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

• Main Authors: Masayuki Yamamoto (Author), Toshihiro Unno (Author), Hayato Matsuyama (Author), Masanobu Kohda (Author), Noriyuki Masuda (Author), Masakazu Nishimura (Author), Toshiaki Ishii (Author), Seiichi Komori (Author)
• Format: Book
• Published: Elsevier, 2008-01-01T00:00:00Z.
• Subjects: article
• Online Access: Connect to this object online.

Summary

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 voltage-clamped 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 glutamate−, respectively, demonstrated that the biphasic current is entirely composed of cation currents. Its initial peak phase was abolished by buffering intracellular Ca2+ to a constant level of 100 nM or depleting intracellular Ca2+ stores, and it was mimicked by the Ca2+ releaser caffeine. Ca2+ 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 [Ca2+]i. These results demonstrate that muscarinic receptor stimulation invokes the openings of two types of cation channel, a Ca2+-activated and a receptor-operated type; the former channels are gated by a rise in [Ca2+]i upon intracellular Ca2+ release, and the latter are gated through other muscarinic receptor-coupled signal transduction mechanisms. Keywords:: cation channel, muscarinic receptor, carbachol, bladder smooth muscle, guinea pig

Item Description

1347-8613
10.1254/jphs.08138FP