Evidence for ryanodine receptors in Schistosoma mansoni

The present study investigated the presence of ryanodine receptors in the trematode Schistosoma mansoni. [H-3]Ryanodine specific binding sites were found in the four subcellular fractions of S. mansoni; however, more binding sites were recovered in the heterogeneous fraction P-1 and the microsomal fraction P-4, as was thapsigargin-sensitive (Ca2+-Mg2+)ATPase activity, marking the sarco/endoplasmic reticulum calcium ATPase (SERCA) pumps. This binding had an equilibrium dissociation constant (K-d) in the nanomolar range, an apparent maximal number of receptors (B-max) of about 80 fmol/mg of protein, and was modulated by ions (Ca2+, Mg2+) and some pharmacological tools such as caffeine. Ryanodine was able to accelerate the rate of Ca-45(2+) release from actively loaded vesicles, and also to induce a transient contraction of the whole worm. We conclude that ryanodine-sensitive Ca2+ release channels are present in S: mansoni, with properties very similar to the ones present in higher animals. (C) 1998 Elsevier Science Inc.