title: Effects of ryanoids on spontaneous and depolarization-evoked calcium release events in frog muscle.
abstract: The effects of ryanoids on calcium sparks and transients were studied in voltage-clamped cut frog muscle fibers with a laser scanning confocal microscope. For each ryanoid employed, several sequential effects were observed, including: a), transient increases in spontaneous spark frequency; b), conversions of sparks to long-lasting steady glows; and c), occasional interruptions of the glows. The ratio of the amplitude of the glow induced by a ryanoid to that of the precursory spark followed the order: ryanodol > ryanodine > C(10)-O(eq)-glycyl-ryanodine > C(10)-O(eq)-beta-alanyl-ryanodol. This sequence of glow amplitudes parallels that of the subconductances induced by these ryanoids in single-channel studies, suggesting that the glows reflect Ca(2+) fluxes through semiopen calcium release channels. Ryanoids also abolished depolarization-evoked sparks elicited with small pulses, and transformed the calcium release during depolarization to a uniform nonsparking fluorescence signal. The ratio of this signal, averaged spatially, to that of the control followed the order: ryanodol < ryanodine < C(10)-O(eq)-glycyl-ryanodine < C(10)-O(eq)-beta-alanyl-ryanodol, implying an inverse relationship with the amplitudes of ryanoid-induced glows. The observation that depolarization-evoked calcium release can occur after ryanoid suppression of calcium sparks suggests the possibility of a new strategic approach for treating skeletal muscle diseases resulting from leaky calcium release channels.
authors.affiliation: Department of Cellular and Integrative Physiology, Indiana University Medical Center, Indianapolis, 46202, USA. cshui@iupui.edu
authors.forename: Chiu Shuen
authors.initials: CS
authors.lastname: Hui
authors.forename: Henry R
authors.initials: HR
authors.lastname: Besch
authors.forename: Keshore R
authors.initials: KR
authors.lastname: Bidasee
mesh_terms: D000470:Alkaloids / Q000494:pharmacology; D000818:Animals; D002118:Calcium / Q000378:metabolism*; D004558:Electric Stimulation; D008333:Mandelic Acids / Q000494:pharmacology; D008564:Membrane Potentials / Q000187:drug effects* / Q000502:physiology; D018613:Microscopy, Confocal; D009119:Muscle Contraction / Q000187:drug effects* / Q000502:physiology; D018482:Muscle, Skeletal / Q000187:drug effects / Q000502:physiology*; D011896:Rana temporaria / Q000502:physiology; D012433:Ryanodine / Q000494:pharmacology*
chemical_list: D000470:Alkaloids; D008333:Mandelic Acids; D012433:Ryanodine; C005419:oxybutynin; D002118:Calcium