Weak electromagnetic fields alter Ca(2+) handling and protect against hypoxia-mediated damage in primary newborn rat myotube cultures.

Abstract

Weak electromagnetic fields (WEF) enhance Ca(2+) entry into cells via voltage-gated Ca(2+) channels and affect various aspects of metabolism, structure, and function. However, little information is available on the effect of WEF on skeletal muscle, which depends primarily on intracellular Ca(2+) stores for function and metabolism. Here, we examine the effects of 30min exposure of rat primary myotube cultures to WEF (1.75μT, 16Hz) on Ca(2+) handling and creatine kinase (CK) release. Free myoplasmic Ca(2+) concentration ([Ca(2+) i]) was measured with the ratiometric dye indo-1. WEF did not affect basal [Ca(2+)]i but decreased the twitch [Ca(2+)]i transient in a time-dependent manner, and the twitch amplitude was decreased to ∼30% after 30min. WEF completely abolished the increase in [Ca(2+)]i induced by potassium chloride (∼60mM) but had no effect on the increase induced by caffeine (∼6mM). Hypoxia (2h exposure to 100% argon) resulted in a marked loss of CK into the medium (400% of normoxic value), as well as a rapid (within 20min) and sustained increase in basal [Ca(2+)]i (∼20% above baseline). However, during exposure to WEF, basal [Ca(2+)]i remained constant during the initial 60min of hypoxia and, thereafter, increased to levels similar to those observed in the absence of WEF. Finally, WEF blocked about 80% of hypoxia-mediated CK release (P < 0.05). These data demonstrate that WEF inhibits increases in [Ca(2+)]i by interfering with muscle excitation and protects against muscle damage induced by hypoxia. Thus, WEF may have therapeutic/protective effects on skeletal muscle.