Comparison of the effect of calcium withdrawal from the medium and of blockade of extracellular calcium entry by isradipine on the contractile responses of the isolated rat stomach.
The role of calcium in drug-induced contractions of rat gastric fundus strips was evaluated by determining the effect of two procedures on the dose-response curves of agonists: a) removal of calcium from the nutrient solution and b) blockade of calcium channels with the dihydropyridine isradipine. Gastric strips were obtained from adult Wistar rats and suspended in Tyrode solution at 37 degrees C for contraction studies. Dose-response curves for carbachol (CCh), serotonin (5-HT), KCl and BaCl2 were constructed under the two conditions described above. A complete blockade of contractile effects was observed for 5-HT and KCl 60 min after calcium withdrawal or after using 3 nM (45 min) of the calcium antagonist. A lower dose of antagonist or a shorter incubation in calcium-free solution caused a partial decrease of dose-response curves, added to a 30-fold shift to the right after the calcium antagonist (1 nM), or a larger than 100-fold shift 3 min after calcium removal. In contrast, dose-response curves for CCh and BaCl2 were not significantly affected by either type of treatment. It is concluded that 5-HT and KCl utilize extracellular sources of calcium, whereas CCh or BaCl2 depends on a tightly-bound calcium pool in this preparation.
Smaili
S S
SS
Departamento de Farmacologia, Escola Paulista de Medicina, São Paulo, Brasil.
Jurkiewicz
N H
NH
Garcia
A G
AG
Jurkiewicz
A
A
D000818:Animals; D002118:Calcium / Q000502:physiology*; D002217:Carbachol / Q000494:pharmacology; D004095:Dihydropyridines / Q000494:pharmacology; D005260:Female; D017275:Isradipine; D008297:Male; D009119:Muscle Contraction / Q000187:drug effects*; D051381:Rats; D011919:Rats, Inbred Strains; D012702:Serotonin Antagonists / Q000494:pharmacology; D013270:Stomach / Q000502:physiology*
D004095:Dihydropyridines; D012702:Serotonin Antagonists; D002217:Carbachol; D002118:Calcium; D017275:Isradipine