title: Potassium, sodium, water, and Donnan potential changes in the myofibrils of intact muscle fibres after exposure to ouabain and K-free Ringer.
abstract: Frog sartorius muscles were superfused for 40 min with solutions of K-free Ringer, normal Ringer containing ouabain, or K-free Ringer containing ouabain. Changes in myoplasmic K and Na were measured with ion-selective microelectrodes; changes in total fibre K and Na were measured by means of atomic absorption spectroscopy; and changes in total fibre water content were obtained from wet and dry weights. Application of a two-compartment model permitted one to calculate (i) the K, Na, and water changes in the myofibrils and in the surrounding myoplasm (extramyofibrillar space); (ii) the changes in the transmyofibrillar Donnan potential (ED); and (iii) the changes in the ratio of the apparent association constants (kNa/kK) of the myofilament charge sites to Na and K. In the resting fibres, the K, Na, and water content of the myofibrils were calculated to be 82, 87, and 80% of total fibre content, respectively; ED was calculated as -4.5 mV; kNa/kK was calculated as 1.4. After a 40-min ouabain treatment, 12 mmol (per kg fibre water) of intrafibre K exchanged with 7.5 mmol of extrafibre Na, 6.4 mmol of myofibrillar K exchanged with an equal amount of extramyofibrillar Na, ED increased to -8.3 mV, and kNa/kK remained relatively constant. After a 40-min K-free treatment, the fibres gained 5.5 mmol of Na without any change in fibre K or water, the myofibrils shifted 9.3% of their water into the extramyofibrillar space instead of exchanging K for Na, ED increased to -10.7 mV, and kNa/kK decreased to 0.47.(ABSTRACT TRUNCATED AT 250 WORDS)
authors.affiliation: Department of Anatomy, Faculty of Health Sciences, University of Ottawa, Ont., Canada.
authors.forename: C N
authors.initials: CN
authors.lastname: Fong
authors.forename: J A
authors.initials: JA
authors.lastname: Hinke
mesh_terms: D000465:Algorithms; D000818:Animals; D004594:Electrophysiology; D007552:Isotonic Solutions; D008839:Microelectrodes; D009210:Myofibrils / Q000187:drug effects / Q000502:physiology*; D010042:Ouabain / Q000494:pharmacology*; D011188:Potassium / Q000378:metabolism*; D011894:Rana pipiens; D012964:Sodium / Q000378:metabolism*; D014867:Water
chemical_list: D007552:Isotonic Solutions; C051865:Krebs-Ringer solution; D014867:Water; D010042:Ouabain; D012964:Sodium; D011188:Potassium