Divergent Effects of Calcium Channel Modulators on H-Reflex Excitability in Fatigued Rat Muscle

TL;DR

This study shows that drugs affecting calcium channels in fatigued rat muscles have different effects on spinal reflex activity, suggesting a link between calcium regulation and muscle performance.

Contribution

The study reveals divergent effects of calcium channel modulators on spinal reflex excitability during muscle fatigue in rats.

Findings

Amiloride and Nifedipine reduced the Hmax/Mmax ratio by 77% and 60%, respectively.

(−)-Bay K8644 increased the Hmax/Mmax ratio by 129%.

Pharmacological modulation of Ca2+ channels has distinct effects on spinal excitability during fatigue.

Abstract

Calcium (Ca2+) release from the sarcoplasmic reticulum is central to excitation–contraction coupling and plays a critical role in the development of skeletal muscle fatigue. Altered Ca2+ dynamics may affect not only contractile function but also neuromuscular excitability. This study examined the effects of pharmacological modulation of Ca2+ channels on fatigue development and spinal reflex activity in rats. Using the Hoffmann reflex (H-reflex) as an indicator of motoneuron excitability, we evaluated the effects of Ca2+ channel blockers (Amiloride, Nifedipine) and an activator ((−)-Bay K8644) on the reflex responses of the plantar muscle before and after fatigue induction. The ratio of the maximum H-reflex to maximum M-wave (Hmax/Mmax) was used to assess alterations in spinal excitability. Compared with the control, both Amiloride and Nifedipine markedly reduce the Hmax/Mmax ratio (77% and 60%, respectively), whereas (−)-Bay K8644 elicited a robust 129% increase. These findings demonstrate that pharmacological modulation of Ca2+ channels has distinct and divergent effects on spinal excitability during fatigue. These results highlight the close interaction between intramuscular Ca2+ regulation and reflex pathways and suggest potential strategies for enhancing muscle performance through targeted Ca2+ channel modulation.

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