Effects of contraction and lactic acid on the discharge of group III muscle afferents in cats

Abstract

1. In barbiturate-anesthetized cats we examined the interaction of lactic acid and static contraction on the discharge of group III muscle afferents. Only afferents whose receptive fields were located in the triceps surae muscles were studied. 2. Twelve of 20 afferents were stimulated by a 60-s static contraction. The majority of firing occurred within the first few seconds of contraction. Thirteen of 20 afferents were stimulated by femoral arterial injections of 24 mM lactic acid (1-4 ml) with the muscle at rest. Repeated injections of lactic acid with the muscle at rest led to tachyphylaxis. Lactic acid was then injected (24 mM; 4 ml) during the last 15 s of static contraction. In eight of nine afferents that were tachyphylactic to lactic acid with the muscle at rest, we noted a restored sensitivity to lactic acid during contraction. 3. In separate experiments we examined the effects of dichloroacetate (DCA) on the responses of group III muscle afferents to static contraction. DCA reduces the production of lactic acid by increasing levels of the active form of the enzyme pyruvate dehydrogenase. 4. DCA lowered arterial and venous lactate concentrations at rest and during contraction. DCA significantly decreased (31%; P < 0.05) the responses of the afferents to contraction. This effect was most prominent within the first 10 s of contraction and was not due to a reduced level of mechanical stimulation after DCA, because peak tension levels were the same during the two bouts of contraction.(ABSTRACT TRUNCATED AT 250 WORDS)

Augmented Mechanical Response of Muscle Thin-Fiber Sensory Receptors Recorded from Rat Muscle–Nerve Preparations In Vitro After Eccentric Contraction

“…The percentage of fibers that responded to acid and lactic acid was smaller (nearly 10 -20%) than we expected (Table 1) based on previous reports: Acidic phosphate buffer (pH 6) directly injected into receptive fields of rat gastrocnemius muscle excited 56.0% of group IV units (Hoheisel et al 2004), and 24 mM lactic acid (1-4 ml) administered intraarterially caused activation of 13 out of 20 group III afferents of cat gastrocnemius muscle (Sinoway et al 1993). The discrepancy between our results and that of others' may have arisen from the application method for the chemicals and from the muscle used.…”

Control of breathing and muscle perfusion in humans

“…The observation that: (I) the stimulation of group I11 and IV muscle afferent fibres increases ventilation (for review see Mitchell & Schinitt, 1983) and (2) both types of afferent fibres are stimulated by intra-arterial injection of substances intended to mimic the local metabolic changes induced by contractions (Mense & Stahnke, 1983;Rotto & Kaufman, 1988;Sinoway et al 1993;Kaufman, 1995), has led to the idea that the chemical changes occurring in an exercising muscle can increase ventilation in proportion to the level of its local metabolic activity (Tibes, 1977;Mitchell & Schmitt, 1983).…”

Exercise pressor reflex in health and diseases: Animal studies

“…Moreover, arachidonic acid 15) and lactic acid 14) infused intra-arterially enhanced the responses of group III muscle afferents to contraction, suggesting their role in sensitizing mechanically sensitive muscle afferents responding to contraction. Finally, a pharmacological blockade of muscle receptors for ATP (purinergic 2X) 16) , bradykinin (B2) 17) and lactic acid 14) or the cyclooxygenase inhibitor 18) reportedly attenuated increases in cat muscle afferent activities in response to contraction.…”

“…1). Intra-arterial infusion into cat hindlimb muscle circulation of ATP 10) , arachidonic acid 11) , bradykinin 12,13) , and lactic acid 11,14) , all of which are byproducts of muscular contraction, were shown to increase discharges of group III and/or IV muscle afferents. Moreover, arachidonic acid 15) and lactic acid 14) infused intra-arterially enhanced the responses of group III muscle afferents to contraction, suggesting their role in sensitizing mechanically sensitive muscle afferents responding to contraction.…”

“…Intra-arterial infusion into cat hindlimb muscle circulation of ATP 10) , arachidonic acid 11) , bradykinin 12,13) , and lactic acid 11,14) , all of which are byproducts of muscular contraction, were shown to increase discharges of group III and/or IV muscle afferents. Moreover, arachidonic acid 15) and lactic acid 14) infused intra-arterially enhanced the responses of group III muscle afferents to contraction, suggesting their role in sensitizing mechanically sensitive muscle afferents responding to contraction. Finally, a pharmacological blockade of muscle receptors for ATP (purinergic 2X) 16) , bradykinin (B2) 17) and lactic acid 14) or the cyclooxygenase inhibitor 18) reportedly attenuated increases in cat muscle afferent activities in response to contraction.…”