EFFECTS OF ASCORBATE ON CONTRACTILE ACTIVITY OF ILEAL SMOOTH MUSCLE

¹ Department of Pharmacology, Tulane University, School of Medicine, New Orleans, Louisiana

Sodium ascorbate (NaAsc) has a complex stimulating action on guinea-pig isolated ileal longitudinal smooth muscle. 1) A direct spasmogenic effect occurs in physiological bathing medium. This effect is mimicked in part by the Ca⁺⁺ chelating agent, disodium ethylenediamine tetraacetic acid but not by calcium ascorbate or the Ca⁺⁺ salt of ethylenediamine tetraacetic acid. It is blocked by Mg⁺⁺. 2) Acetylcholine (ACh)-induced contractions in physiological bathing solution are potentiated by NaAsc. 3) NaAsc opposes the development of ACh-desensitization in tissues bathed in physiological medium. These various stimulatory effects of ascorbate may involve an interaction with Ca⁺⁺ stabilizing the muscle cell membrane or serving as activator ions. Some evidence for such an interaction has been obtained. a) Tissues previously exposed to NaAse respond more vigorously than untreated muscles when graded concentrations of CaCl₂ are added to a bathing solution devoid of Ca⁺⁺ and containing a high level of ACh. b) NaAsc tends to oppose the secondary ACh-induced depression of the contractile responses of Ca⁺⁺-loaded tissues abruptly transferred to Ca⁺⁺-free medium. c) Muscle strips from ascorbate-deprived animals exhibit less contraction when transferred to Ca⁺⁺-free solution after Ca⁺⁺ loading than tissues from animals fed a normal diet.