AJP - Gastrointestinal and Liver Physiology, Vol 262, Issue 5 940-G944, Copyright © 1992 by American Physiological Society
Interaction between carbachol and vasoactive intestinal peptide in cells of isolated colonic crypts
L. Greenwald and B. A. Biagi
Department of Zoology, Ohio State University, Columbus 43210.
In a previous study [B. Biagi, Y.-Z. Wang, and H. J. Cooke, Am. J. Physiol.
258 (Gastrointest. Liver Physiol. 21): G223-G230, 1990], carbachol
stimulated active chloride transport in rabbit distal colon, yet had no
effect on the basolateral membrane potential (Vbl) of cells from isolated
crypts from the same tissue. In the present study, crypt cells were first
depolarized with vasoactive intestinal peptide (VIP; 1 x 10(-9) M) (control
Vbl = -62 mV; VIP Vbl = -48 mV) and then exposed to carbachol in the
presence of VIP. The VIP-induced depolarization of Vbl was completely
reversed by carbachol (0.1 mM; repolarization to -65 mV). Similar
repolarization was seen by applying carbachol to crypt cells depolarized by
10 mM aminophylline. Intracellular K+ activity (aiK), measured with
K(+)-selective microelectrodes, was 64.3 mM (concn = 85 mM), yielding a K+
equilibrium potential (EK+) of -76 mV. Neither carbachol nor VIP
application caused significant changes in aiK. These results demonstrate
the presence of cholinergic receptors on colonic crypt cells. The magnitude
of the carbachol effect on Vbl is greater when Vbl is depolarized relative
to EK+. The results are consistent with the hypothesis that carbachol acts
by increasing basolateral K+ conductance, driving the cell toward the EK+.
