Extracellular H+ modulates acetylcholine-activated nonselective cation channels in guinea pig ileum
Inoue, R.; Waniishi, Y.; Ito, Y.
American Journal of Physiology 268(1 Pt 1): C162-C170
1995
ISSN/ISBN: 0002-9513 PMID: 7530907 Document Number: 446461
The effects of external H+ on the acetylcholine-induced inward current (nonselective cationic current; I-nsACh) in guinea pig ileal smooth muscle were investigated using the conventional whole cell patch-clamp technique. When the external pH (pH-o) was lowered, the amplitude of I-nsACh was increased, with no significant change in the reversal potential or no detectable induction of other ionic permeabilities. The dose-response curve for this effect was best described by a Hill-type equation with an apparent pK-a value of 7.4 and a Hill coefficient of apprx 1. The effect of pH-o was associated with a shift of the steady-state activation curve for I-nsACh; the half-maximum activation potential became more negative on lowering pH-o. Similar results were obtained when I-nsACh was activated by intracellularly applied guanosine 5'-O-(3-thiotriphosphate). These results indicate that the external H+ activity is an efficient regulator of I-nsACh channel, and this may have a physiological importance for controlling the muscarinic receptor-mediated contractions in this muscle.