title: The effect of praziquantel on calcium in Hymenolepis diminuta.
abstract: Praziquantel (PZ) at concentrations down to 5 x 10(-8) M induced a rapid contraction of Hymenolepis diminuta musculature. This effect was accompanied by a strong inhibition of 45Ca2+ incorporation which showed some dependence on Ca2+ concentration. Ca2+ efflux experiments showed that PZ markedly stimulated the release of Ca2+ from tapeworms preloaded with 45Ca2+, with the effluxed Ca2+ being derived from a small fast pool and a larger slow pool. This stimulatory effect appeared., like PZ-induced muscle contraction, to be independent of external Ca2+. By carrying out 45Ca2+ exchange experiments under near equilibrium conditions and atomic absorption spectroscopy it could be demonstrated that PZ resulted in a net excretion of endogenous Ca2+. In PZ-induced contracted worms adenylate nucleotide levels and the adenylate energy charge were not significantly different from those of untreated control worms. Also, PZ had no effect on Ca2+-stimulated ATPase activity of the tapeworm's tegumental brush border. Nor did the drug alter the activities of Ca2+-ATPases in whole homogenates of worms or mitochondria, microsomal or soluble fractions. Although the mechanism of PZ-induced changes in Ca2+ transport was not elucidated, it is suggested that the sustained release of endogenous Ca2+ may affect the sequence of excitation-contraction coupling and that such interference may cause the observed massive contraction of the tapeworm's musculature.
mesh_terms: D000227:Adenine Nucleotides / Q000378:metabolism; D000818:Animals; D001692:Biological Transport / Q000187:drug effects; D002118:Calcium / Q000378:metabolism*; D000252:Calcium-Transporting ATPases / Q000378:metabolism; D006926:Hymenolepis / Q000187:drug effects* / Q000378:metabolism; D007546:Isoquinolines / Q000494:pharmacology*; D007700:Kinetics; D008871:Microvilli / Q000201:enzymology; D008928:Mitochondria / Q000201:enzymology; D009119:Muscle Contraction / Q000187:drug effects; D011223:Praziquantel / Q000494:pharmacology*
chemical_list: D000227:Adenine Nucleotides; D007546:Isoquinolines; D011223:Praziquantel; D000252:Calcium-Transporting ATPases; D002118:Calcium