Contractions of the filariidAcanthocheilonema viteae induced by potassium chloride

Abstract

The effects of K⁺ on muscle contractility were explored in the filarial nematodeAcanthocheilonema viteae (Dipetalonema viteae). The parasite was slit open longitudinally and mounted in a smooth muscle chamber that was filled with aerated (95% N₂−5% CO₂) physiological solution at 37°C. KCl at concentrations ranging from 20 to 100 mM induced a rapid isotonic contraction of the filarial muscle. The maximal response from KCl was similar to the maximal response to acetylcholine chloride (ACh). When KCl was applied for several minutes, tolerance frequently occurred. Contractions were also induced by K₂SO₄ but not by NaCl, Na₂SO₄ or sucrose. Nifedipine was more than 10 times as potent in reducing the KCl-induced contraction as in reducing that caused by ACh. The KCl-induced contraction was abolished in a Ca-free physiological medium containing ethyleneglycol-bis-(β-aminoethyl ether)N,N,N′,N′-tetraacetic acid (EGTA, 10⁻⁴ M). Low [Ca²⁺]/[Mg²⁺] solutions blocked the spontaneous activity, the KCl-induced contractions, and the ACh-induced contractions. KCl also induced contractions in denervated muscle strips, supporting the hypothesis that K⁺ acts directly on the muscle cells. These results indicate that K⁺ can depolarize the muscle membrane and induce a muscle contraction that is dependent on extracellular calcium ions.