Schistosoma mansoni: myogenic characteristics of phorbol ester-induced muscle contraction.

The myogenic nature of phorbol ester-induced muscle contractures of Schistosoma mansoni was investigated using muscle physiology and electrophysiological techniques. The contracture is dependent of extracellular Ca2+, is blocked by Ca2+ channel blockers, and appears to be associated with an increase in the permeability of the muscle to Ca2+ but not to Na+ or H+. The musculature is not depolarized during phorbol ester-induced contracture, but surface electrical activity decreases. Threshold treatments of phorbol ester and depolarization or praziquantel produce synergistic contractures of the parasite. The contracture could not be explained by altered release of or sensitivity to putative neurotransmitters, decreased Ca2+ efflux, or an increase in the sensitivity of the contractile system to Ca2+. These results support the hypothesis that activation of protein kinase-C in the schistosome with phorbol esters leads to muscle contracture by enhancing sarcolemmal Ca2+ channel activity.