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Original articles  EXERCISE PHYSIOLOGY AND BIOMECHANICS 

The Journal of Sports Medicine and Physical Fitness 2002 December;42(3):418-24

Copyright © 2009 EDIZIONI MINERVA MEDICA

lingua: Inglese

The effect of L-(+)-lactate on tension development and excitability in in vitro rat diaphragm muscle

Erdog¸an S¸., Kurdak S. S., Ergen N., Dog¸an A.

Department of Physiology, Faculty of Medicine University of Çukurova, Adana, Turkey


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Back­ground. The aim of ­this ­study was to deter­mine the ­effect of lac­tate ­anion, inde­pen­dent of H+, on in ­vitro rat dia­phragm ­muscle ten­sion devel­op­ment, and to eval­uate the ­changes in excit­ability by meas­uring ­resting mem­brane poten­tial (RMP) and the ampli­tude of the sar­co­lemma ­action poten­tial (AP).
­Methods. Dia­phragm ­muscle ­strips ­taken ­from ­5 ­Wistar ­strain ­albino ­rats ­were ­placed in a ­tissue ­bath aer­ated ­with 95% O2 and 5% CO2 con­tin­u­ously at 30°C. The ­muscle was ­attached to an iso­metric ­force trans­ducer and stim­u­lated indi­rectly by the ­phrenic ­nerve (0.2 msec, 0.5 Hz, and supra­max­i­mally). Two ­groups ­were ­studied, ­each sub­jected to a dif­ferent ­sequence of 20 ­min expo­sures to a ­high ­level of lac­tate (­high [La]), (20 mM) or con­trol ­periods (C) ­without lac­tate. The ­first ­group was sub­jected to (C, ­high [La], C), and the ­second was sub­jected to (­high [La], C, ­high [La]). Fol­lowing the prep­ar­a­tion of ­high [La] solu­tion, pH was ­adjusted by ­adding sat­u­rated ­NaOH. In the ­second ­part of ­this experi­ment con­ven­tional micro­elec­trode tech­nique was ­used to deter­mine the RMP and ampli­tude of sar­co­lemma AP of the rat dia­phragm ­muscle. Thir­teen mus­cles ­were ­used and 20-30 meas­ure­ments ­were per­formed in ­both C and ­high [La] ­groups.
­Results. Addi­tion of lac­tate ­reduced the ­mean ten­sion devel­op­ment sig­nif­i­cantly (p<0.05) at ­isopH (pH was 7.34±0.001 for C vs 7.33±0.001 for ­high [La]). ­Mean ­values of RMP (84.29±0.29 mV for C, -84.82±0.28 mV for ­high[La]) and ampli­tude of sar­co­lemma AP (118.86±0.72 mV for C, 119.19±0.71 mV for ­high[La]) did not ­differ sig­nif­i­cantly.
Con­clu­sions. We con­clude ­that lac­tate ­reduces ten­sion devel­op­ment at iso-pH ­without ­altering the ampli­tude of sar­co­lemma AP and RMP.

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