AJP - Gastrointestinal and Liver Physiology, Vol 238, Issue 6 520-G525, Copyright © 1980 by American Physiological Society
Effect of external ions on 45Ca efflux from cat intestinal muscle
B. A. Curtis, D. Kreulen and C. L. Prosser
The surface-bound Ca of isolated circular smooth muscle of cat small
intestine can be removed by substitution of LiCl for NaCl in Krebs
solution. This substitution removed surface-bound Ca (45Ca) and allowed us
to study transmembrane 45Ca efflux. Neither the resting membrane potential
nor contractility changed when Li was substituted for Na. Li removed the
same extracellular 45Ca store as did ethylene
glycol-bis-(beta-aminoethylether)-N,N'-tetraacetic acid. The resting
transmembrane 45Ca efflux was inhibited by La3+ and was unchanged in Li,
tris(hydroxymethyl)aminomethane, arginine, and sucrose Krebs solution. The
extra 45Ca efflux observed upon electrical stimulation was no greater in
Na-Krebs than Li-Krebs, but during response to acetylcholine the extra 45Ca
efflux was greater in Na-Krebs than Li-Krebs. We conclude that the
surface-bound Ca is sensitive to external Na and that the transmembrane Ca
efflux is not completely dependent on external Na.
