Effects of ionophore A23187 and lanthanum on pepsinogen secretion from frog esophageal mucosa in vitro.
The role of Ca2+ in the mediation of pepsinogen secretion from frog esophagus was investigated by means of ionophore A23187 and LaCl3. The esophageal mucosa from Asian bullfrog Rana tigerina was mounted in a double-chamber system to preserve its polarity and was incubated in a medium containing 1.5 mM CaCl2. Pepsinogen secreted was measured and expressed as % of total. The basal secretion averaged 3.5%/h. Bethanechol (25 microM), dibutyryl-cAMP (10 mM), ionophore A23187 (30 microM) and 3-isobutyl-1-methylxanthine (0.1 mM) increased the secretion to 8.7, 7.4, 7.1 and 6.8%, respectively. The stimulatory effect of bethanechol and of dibutyryl-cAMP were not affected by removing the exogenous Ca2+ with EGTA. The basal secretion was, however, reduced by 50% when Ca2+ in the incubation medium was lowered to 20 microM. At this low Ca2+ concentration, ionophore A23187 not only lost its stimulatory effect but also diminished the stimulation caused by bethanechol and dibutyryl-cAMP. While LaCl3 at 1 mM had no effect on basal and bethanechol-stimulated secretion, at 10 mM it abolished the stimulation evoked by bethanechol or dibutyryl-cAMP. The conclusions are: (1) both Ca2+ and cAMP are involved in the mediation of pepsinogen secretion from frog esophagus, (2) basal secretion is dependent on extracellular Ca2+, whereas bethanechol-stimulated secretion is not, (3) in the plasma membranes of peptic cells may exist a distinct Ca2+ pool (La3+-and ionophore A23187-sensitive) which is involved in the stimulated pepsinogen secretion.
Fong
J C
JC
D015056:1-Methyl-3-isobutylxanthine / Q000494:pharmacology; D000818:Animals; D018723:Bethanechol; D001626:Bethanechol Compounds / Q000494:pharmacology; D003994:Bucladesine / Q000494:pharmacology; D000001:Calcimycin / Q000494:pharmacology*; D004947:Esophagus / Q000378:metabolism*; D007811:Lanthanum / Q000494:pharmacology*; D009092:Mucous Membrane / Q000378:metabolism; D010435:Pepsinogens / Q000378:metabolism*; D011898:Ranidae; D013997:Time Factors
D001626:Bethanechol Compounds; D010435:Pepsinogens; D018723:Bethanechol; D000001:Calcimycin; D003994:Bucladesine; D007811:Lanthanum; D015056:1-Methyl-3-isobutylxanthine