L- and DL-carnitine induce tetanic fade in rat neuromuscular preparation

Abstract

Carnitine, a structurally choline-like metabolite, has been used to increase athletic performance, although its effects on neuromuscular transmission have not been investigated. It is present in skeletal muscle and its plasma levels are about 30 to 90 µM. Using rat phrenic nerve diaphragm preparations indirectly and directly stimulated with high rate pulses, D-carnitine (30 and 60 µM), L-carnitine (60 µM) and DL-carnitine (60 µM) were shown to induce tetanic fade (D-carnitine = 19.7 ± 3.1%, N = 6; L-carnitine = 16.6 ± 2.4%, N = 6; DL-carnitine = 14.9 ± 2.1%, N = 6) without any reduction of maximal tetanic tension. D-carnitine induced tetanic fade in neuromuscular preparations previously paralyzed with d-tubocurarine and directly stimulated. The effect was greater than that obtained by indirect muscle stimulation. Furthermore, previous addition of atropine (20 to 80 µM) to the bath did not reduce carnitine isomer-induced tetanic fade. In contrast to D-carnitine, the tetanic fade induced by L-and DLcarnitine was antagonized by choline (60 µM). The combined effect of carnitine isomers and hemicholinium-3 (0.01 nM) was similar to the effect of hemicholinium-3 alone. The data suggest that L-and DLcarnitine-induced tetanic fade seems to depend on their transport into the motor nerve terminal.

Effects of oral L-carnitine and DL-carnitine supplementation on alloxan-diabetic rats

“…Therefore, as described in other studies (Paulson and Shug 1981;Bremer 1983), the liver pool of LC appeared to be less affected by the D-carnitine (DC). Therefore, the results from non-diabetic rats suggested the existence of selectivity to the LC isomer (Huth and Shug 1980;Vary and Neely 1982;Lopes et al 2003). In agreement with this proposition, several studies showed the existence of a competitive inhibition of the LC uptake by the DC (Yokogawa et al 1999;Georges et al 2000.…”

Tetanic Facilitation of Neuromuscular Transmission by Adenosine A_2A and Muscarinic M₁ Receptors is Dependent on the Uptake of Choline via High-Affinity Transporters

“…HC-3 (4-10 µmol/L) was applied in a cumulative manner and contacted the preparations at least for 45 min before any valid myographic recording was obtained. This protocol was adopted, since HC-3 effects following each bath application required roughly 45 [FSK] and NEO) were applied 20 min after starting the HC-3 application and, thus, contacted with the preparations for at least 25 min. For comparison purposes, the paradoxical inhibitory effect of NEO on tetanic tension was also tested 40 min after selectively blocking the α3β2-subunit nicotinic receptor with hexamethonium (HEX) and/or the muscarinic M 2 receptor with Meth.…”

Efectos de la suplementación de carnitina sobre el nivel de fatiga muscular del gastrocnemio de ratas entrenadas y sedentárias

“…En consecuencia, la carnitina juega un papel importante en el proceso de β-oxidación mitocondrial 10 , pudiendo ser usada para incrementar el rendimiento atlético y mantener una carga determinada de trabajo 10 ; pero ese efecto sobre la transmisión neuromuscular aún no fue muy investigado 11 , inclusive se sabe muy poco en relación al efecto del entrenamiento sobre el contenido de L-carnitina en las células musculares 12 y merece ser estudiado. Por lo tanto, el objetivo del presente estudio fue determinar el efecto de la suplementación de L-carnitina sobre el nivel de fatiga muscular del músculo gastrocnemio de ratas sedentarias y entrenadas.…”