CHARACTERIZATION OF THE RYANODINE RECEPTOR CHANNEL OF INVERTEBRATE MUSCLE/

Electron-microscopic analysis was used to show that invertebrate muscl e has feetlike structures on the sarcoplasmic reticulum (SR) displayin g the-typical four-subunit appearance of the calcium (Ca2+) release ch annel/ryanodine receptor (RyR) observed in vertebrate skeletal muscle (K. E. Loesser, L. Castellani, and C. Franzini-Armstrong. J. Muscle Re s. Cell Motil. 13: 161-173, 1992). SR vesicles from invertebrate muscl e exhibited specific ryanodine binding and single channel currents tha t were activated by Ca2+, caffeine, and ATP and inhibited by ruthenium red. The single channel conductance of this invertebrate RyR was lowe r than that of the vertebrate RyR (49 and 102 pS, respectively). Activ ation of lobster and scallop SR Ca2+ release channel, in response to c ytoplasmic Ca2+ (1 nM-10 mM), reflected a bell-shaped curve, as is fou nd With the mammalian RyR. In contrast to a previous report (J.-H. Seo k, L. Xu, N. R. Kramarcy, R. Sealock, and G. Meissner. J. Biol. Chem. 267: 15893-15901, 1992), our results show that regulation of the inver tebrate and vertebrate RyRs is quite similar and suggest remarkably si milar paths in these diverse organisms.