Role of calcium in chloride secretion mediated by cAMP pathway activation in rabbit distal colon mucosa.
Effects of Ca2+ on adenosine 3',5'-cyclic monophosphate (cAMP)-mediated Cl- secretion were investigated in intact mucosa and isolated crypt cells of rabbit descending colon. Addition of 10 microM prostaglandin (PG)E2 or forskolin to tissues incubated in Ca(2+)-free medium increased the size of short-circuit current (Isc) and Cl- secretion as estimated by unidirectional 36Cl flux measurements (net flux = -2.31 +/- 0.24 vs. -1.22 +/- 0.10 mueq.h-1.cm-2, n = 4, P < 0.001). Addition of 10 microM PGE2 to tissues incubated in 1.2 mM Ca2+ Ringer induced a 7-fold increase in mean cAMP level, whereas it produced an 11-fold increase in tissues exposed to Ca(2+)-free medium. Membrane preparations from whole mucosa incubated in Ca(2+)-free medium displayed a cyclic nucleotide phosphodiesterase activity significantly lower than controls (18.76 +/- 0.54 vs. 31.20 +/- 0.39 pmol cAMP. mg protein-1.min-1, means +/- SE, n = 4, P < 0.001). Ca2+ removal also affected adenylate cyclase (AC) responsiveness to agonists; AC activity increased in controls by 54 and 226% after stimulation with 10 microM PGE2 and forskolin, respectively, but it increased more (77 and 325%, respectively) after incubation in Ca(2+)-free solutions.(ABSTRACT TRUNCATED AT 250 WORDS)
Calderaro
V
V
Institute of Pharmacology and Toxicology, First Faculty of Medicine, University of Naples, Italy.
Chiosi
E
E
Greco
R
R
Spina
A M
AM
Giovane
A
A
Quagliuolo
L
L
Servillo
L
L
Balestrieri
C
C
Illiano
G
G
D000262:Adenylyl Cyclases / Q000378:metabolism; D000818:Animals; D002118:Calcium / Q000502:physiology*; D002712:Chlorides / Q000378:metabolism*; D003106:Colon / Q000378:metabolism*; D000242:Cyclic AMP / Q000378:metabolism*; D004594:Electrophysiology; D007413:Intestinal Mucosa / Q000378:metabolism*; D008297:Male; D009994:Osmolar Concentration; D010727:Phosphoric Diester Hydrolases / Q000378:metabolism; D011817:Rabbits
D002712:Chlorides; D000242:Cyclic AMP; D010727:Phosphoric Diester Hydrolases; D000262:Adenylyl Cyclases; D002118:Calcium