title: A study of the short-term effects of glucose 6-phosphate on the contractile activation properties of skinned single muscle fibres of the rat. Implications for solution design.
abstract: The present study highlights possible problems that can arise from the incorrect preparation of control and test solutions for use in Ca2+-activation experiments using single skinned skeletal muscle fibres and EGTA-based Ca2+ buffers. We show here, using glucose 6-phosphate (G6-P) as our "test" compound, that the Ca2+-activation properties of skinned single fibre segments from the extensor digitorum longus muscle of the rat are highly dependent on the form in which the G6-P is added and on the correct balancing of an appropriate anion in control solutions. Test solutions prepared by the direct addition of 10 mM monosodium G6-P salt to a set of control solutions of defined pCa resulted in significantly greater submaximal force responses than the corresponding controls. This is equivalent to an increase in the sensitivity of the contractile-regulatory system to Ca2+ (pCa50=-log10[Ca2+] that produces 50% of maximum force) by 0.19+/-0.01 pCa units. In contrast, addition of disodium G6-P to control solutions caused a slight reduction in the apparent sensitivity of the contractile apparatus to Ca2+ by 0.04+/-0.01 pCa units (P<0.01). Rather than being indicative of the effects of G6-P on the contractile apparatus, these opposing effects are due to differences between test and control solutions with respect to pH and Na+ concentration brought about by the G6-P salts. When all ionic species were carefully balanced, 10 mM G6-P was found to have only a small sensitizing effect on Ca2+-activation properties compared to control, without affecting the maximum Ca2+-activated force response. Our findings highlight the often-overlooked need for careful balancing of the ionic composition in control and test solutions when examining the true effects of different compounds on the Ca2+-activation characteristics of single skinned muscle fibre preparations.
authors.affiliation: School of Zoology, Faculty of Science and Technology, La Trobe University, Bundoora, Victoria, Australia. M.Patterson@zoo.latrobe.edu.au
authors.forename: M F
authors.initials: MF
authors.lastname: Patterson
authors.forename: G M
authors.initials: GM
authors.lastname: Stephenson
authors.forename: D G
authors.initials: DG
authors.lastname: Stephenson
mesh_terms: D000818:Animals; D002118:Calcium / Q000378:metabolism; D004533:Egtazic Acid; D019298:Glucose-6-Phosphate / Q000494:pharmacology*; D006863:Hydrogen-Ion Concentration; D008297:Male; D009119:Muscle Contraction / Q000187:drug effects*; D018485:Muscle Fibers, Skeletal / Q000187:drug effects* / Q000502:physiology*; D018482:Muscle, Skeletal / Q000187:drug effects / Q000502:physiology; D009994:Osmolar Concentration; D051381:Rats; D020318:Rats, Long-Evans; D012964:Sodium / Q000008:administration & dosage; D012996:Solutions
chemical_list: D012996:Solutions; D004533:Egtazic Acid; D019298:Glucose-6-Phosphate; D012964:Sodium; D002118:Calcium