title: Inositol 1,4,5-trisphosphate-induced Ca2+ release from the sarcoplasmic reticulum and contraction in crustacean muscle.
abstract: Intracellular applications of a fixed amount (0.2 to 8 nmol) of inositol 1,4,5-trisphosphate (InsP3) over a brief period (2 s) into barnacle muscle fibers induced vigorous contractures. Peak tension attained during the first application depended on [InsP3]: the maximum tension evoked by the injection of 8 nmol was 1.6 kg/cm2. Peak tension during a second application of a high dose of InsP3 (greater than 10 microM) was always smaller than that during the first application. Extracellular Ca2+ could be omitted with no measurable effects on either the amplitude or time course of the contractures evoked by InsP3. Aequorin was used to measure InsP3-evoked Ca2+ release from intracellular stores in minced muscle fibers from lobster and in skinned muscle fibers from barnacle. Provided the sarcoplasmic reticulum was preloaded with Ca2+, application of InsP3 induced a transient Ca2+ release that was [InsP3] dependent. During each transient, [Ca2+] rose rapidly to a peak value (t1/2 less than 5 s) and then slowly returned (t1/2 less than 100 s) to a basal level. Maximum Ca2+ release was obtained at [InsP3] less than 100 microM and amounted to 4 nmol Ca2+/g of muscle, enough to increase [Ca2+]i from 0.1 to 8 microM had the Ca2+ release occurred in the intact fiber. Successive applications of a fixed amount of InsP3 elicited successive transient increases in Ca2+. The effects of [Ca2+] on the incorporation of [3H]inositol into the pools of phosphatidylinositol, phosphatidylinositol 4-phosphate, and phosphatidylinositol 4,5-bisphosphate pools were measured.(ABSTRACT TRUNCATED AT 250 WORDS)
mesh_terms: D000818:Animals; D002110:Caffeine / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism* / Q000494:pharmacology; D015544:Inositol 1,4,5-Trisphosphate; D007295:Inositol Phosphates / Q000494:pharmacology*; D007473:Ion Channels / Q000502:physiology; D009119:Muscle Contraction / Q000187:drug effects*; D009132:Muscles / Q000502:physiology*; D019269:Phosphatidylinositol 4,5-Diphosphate; D018129:Phosphatidylinositol Phosphates; D010716:Phosphatidylinositols / Q000096:biosynthesis; D011188:Potassium / Q000494:pharmacology; D012519:Sarcoplasmic Reticulum / Q000187:drug effects / Q000378:metabolism*; D013403:Sugar Phosphates / Q000494:pharmacology*; D001468:Thoracica / Q000502:physiology*
chemical_list: D007295:Inositol Phosphates; D007473:Ion Channels; D019269:Phosphatidylinositol 4,5-Diphosphate; D018129:Phosphatidylinositol Phosphates; D010716:Phosphatidylinositols; D013403:Sugar Phosphates; C037178:phosphatidylinositol 4-phosphate; D002110:Caffeine; D015544:Inositol 1,4,5-Trisphosphate; D011188:Potassium; D002118:Calcium