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

ABSTRACT

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 degrees 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.