Participation of extracellular calcium in α-hederin-induced contractions of rat isolated stomach strips

Abstract

Ethnopharmacological relevanceThe dry extract of Hedera helix leaves, due to its secretolytic and antispasmodic effects, is commonly used to produce pharmaceuticals applied in case of cough and other respiratory symptoms. The results of some in vitro studies as well as the clinical signs of poisoning caused by Hedera helix suggest however strong contractile effect on smooth muscle. In order to clarify the impact of α-hederin (the main active agent of ivy extract) on smooth muscle, the origin of activated calcium involved in α-hederin-induced contraction of gastric smooth muscle preparations was studied. Materials and methodsThe study was carried out on rat isolated stomach corpus and fundus strips, under isotonic conditions. The effect of α-hederin (100μM) on smooth muscle preparations was measured before and after the treatment with verapamil during the incubation in modified Krebs–Henseleit solution (M K–HS). Besides, the effect of saponin was measured during the incubation of preparation in Ca2+-free modified Krebs–Henseleit solution or Ca2+-free EGTA-containing modified Krebs–Henseleit solution. ResultsThe obtained results revealed that the application of verapamil significantly inhibited the reaction evoked by α-hederin. The incubation of stomach strips in calcium-free modified Krebs–Henseleit solution did not change the force of the observed contraction in comparison to the reaction of the preparations incubated in regular incubation solution (M K–HS). In contrary, the replacement of M K–HS by calcium-free chelator-containing solution inhibited totally the reaction to α-hederin. ConclusionsThe results indicated that α-hederin-induced contraction results from the influx of calcium which is located in intercellular spaces or bound to the outside of the cell membrane. The Ca2+ influx occurs predominantly through voltage-dependent calcium channels of L-type.