Preferential potentiation by hypotonic cell swelling of muscarinic
cation current in guinea- pig ileal smooth muscle.
Waniishi, Yoshiki, Ryuji Inoue, and Yushi Ito.
Department of Pharmacology, Faculty of Medicine and the 2nd
Department of Oral and Maxillofacial Surgery, Faculty of Dentistry,
Kyushu University, Fukuoka 812-82, JAPAN
APStracts 3:0231C, 1996.
The effects of hypotonic cell swelling (HCS) on muscarinic receptor
-activated cationic current in guinea-pig ileal smooth muscle were
investigated by the whole-cell patch clamp technique. With nystatin
-perforated recording, reduced external tonicity from 312 to 262mOsm
caused cell swelling, but hardly affected the membrane currents
activated by depolarization such as outward-rectifying K and voltage
-dependent Ca currents. In contrast, the inward current evoked by
carbachol at -60mV was greatly increased (ca. 50%) by the same extent
of hypotonicity. This effect is likely to occur through potentiation
of nonselective cation channels coupled to the muscarinic receptor
(mNSCCs), and probably does not involve elevated intracellular Ca2+
concentration ([Ca2+]i), since neither removal of external Ca2+ nor
[Ca2+]i buffering with 10mM BAPTA significantly affected the results.
Furthermore, the time course and degree of this potentiation closely
matched those of video-microscopically monitored HCS. These results
support the view that mechanosensitive modulation may be a powerful
mechanism to regulate mNSCCs activity in gut smooth muscle, together
with membrane potential and [Ca2+]i.
Received 22 January 1996; accepted in final form 10 July 1996.
APS Manuscript Number C41-6.
Article publication pending Am. J. Physiol. (Cell Physiology).
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 25 July 1996