title: Free calcium in sheep cardiac tissue and frog skeletal muscle measured with Ca2+-selective microelectrodes.
abstract: Microelectrodes filled with neutral carrier selective to Ca2+ were used to measure the free intracellular Ca2+ concentration [( Ca2+]i) in sheep cardiac tissue and frog skeletal muscle. Calibration of the electrodes was performed in the presence of a solution resembling the cationic composition of the cytoplasm. [Ca2+]i at rest in normal physiological saline (20-22 degrees C) was 240 nM in Purkinje fibres, 270 nM in ventricular muscle, and 52 nM in skeletal muscle. In Purkinje fibres, elevation of [Ca2+]o from 1.8 mM to 5.4 mM produced a 1.7-fold increase in [Ca2+]i. Elevation of [Ca2+]o from 1.8 mM to 18 mM induced a 2.6-fold increase in [Ca2+]i. Exposure to Na+-free solution (Li+-substituted) gave rise to elevation of [Ca2+]i by factors of 5.8 and 14 in ventricular muscle and Purkinje fibres, respectively. These latter changes in [Ca2+]i were associated with the development of contractures which reached 34% and 172% of the corresponding twitch tension.
mesh_terms: D000818:Animals; D002118:Calcium / Q000032:analysis* / Q000494:pharmacology; D004533:Egtazic Acid / Q000494:pharmacology; D006352:Heart Ventricles / Q000032:analysis; D008564:Membrane Potentials / Q000187:drug effects; D008839:Microelectrodes; D009132:Muscles / Q000032:analysis*; D009200:Myocardial Contraction / Q000187:drug effects; D009206:Myocardium / Q000032:analysis*; D011690:Purkinje Fibers / Q000032:analysis; D011896:Rana temporaria; D012756:Sheep
chemical_list: D004533:Egtazic Acid; D002118:Calcium