title: Effects of 3,4-diaminopyridine on myoplasmic calcium and phosphoinositide hydrolysis in frog sartorius muscle fibers.
abstract: Using Ca(2+)-selective microelectrodes, the effects of 3,4-diaminopyridine (DAP) on myoplasmic calcium ([Ca2+]i) were studied in frog satorius muscle fibers. DAP induced an increase of [Ca2+]i in a concentration-dependent manner. DAP 1 mmol.L-1 increased the [Ca2+]i from control 166 +/- 41 nmol.L-1 to 416 +/- 69 nmol.L-1 (n = 10). In the absence of external calcium, DAP still enhanced [Ca2+]i. [Ca2+]i of the fibers bathed in Ca(2+)-free Ringer's solution containing DAP 1 mmol.L-1 was 152 +/- 43 nmol.L-1, which was significantly higher than 77 +/- 35 nmol.L-1 of [Ca2+]i of the fibers in Ca(2+)-free Ringer's solution. In addition, DAP promoted the hydrolysis of phosphoinositides, and DAP-induced hydrolysis was more in the presence of external calcium. It is suggested that, through enhancing the hydrolysis of phosphoinositides, DAP released Ca2+ from intracellular Ca2+ store in frog sartorius muscle fibers.
authors.affiliation: Shanghai Institute of Physiology, Chinese Academy of Sciences.
authors.forename: Z M
authors.initials: ZM
authors.lastname: Xu
authors.forename: Z
authors.initials: Z
authors.lastname: Dong
authors.forename: P H
authors.initials: PH
authors.lastname: Zhu
mesh_terms: D015761:4-Aminopyridine / Q000031:analogs & derivatives* / Q000494:pharmacology; D000077770:Amifampridine; D000818:Animals; D002118:Calcium / Q000378:metabolism*; D004305:Dose-Response Relationship, Drug; D006868:Hydrolysis / Q000187:drug effects; D009132:Muscles / Q000378:metabolism; D010716:Phosphatidylinositols / Q000378:metabolism*; D015221:Potassium Channels / Q000187:drug effects; D011898:Ranidae
chemical_list: D010716:Phosphatidylinositols; D015221:Potassium Channels; D015761:4-Aminopyridine; D000077770:Amifampridine; D002118:Calcium