Fluvastatin Alters Both The Calcium Homeostasis And Cell Proliferation In Cultured Myotubes And The Calcium Release Events In Adult Muscle Fibers Of The Rat

Abstract

Skeletal muscle cells of newborn rats were cultured in the absence and presence of fluvastatin (0.1 μM). Resting levels of intracellular calcium concentration ([Ca2+]i) were determined from Fura-2 fluorescence while proliferation was assessed by counting the number of nuclei in myogenic cells. The presence of the drug did not alter [Ca2+]i (130±11 vs 121±7 nM; n=12 vs 10 rats; mean±SE; control and treated, respectively) but reduced the number of myogenic nuclei by 50% after 24 hours of treatment. To assess the chronic effects of fluvastatin on skeletal muscles of adult animals, female rats were kept on diets that either contained 62.5 mg/kg (daily intake 6 mg/kg body weight) fluvastatin or not. Animals were either fed with an otherwise normal chow or with a chow that induced an increase in blood cholesterol. Similarly to cultured cells, [Ca2+]i of adult fibers was unaltered by the drug, however, a clear reduction of muscle mass was observed. Single fibers were enzymatically isolated from the m. extensor digitorum communis, permeabilized with Saponin and loaded with Fluo-4. Calcium release events (CRE) were captured using laser scanning confocal microscopy and analyzed with an automated computer program. Fluvastatin increased the frequency of CRE on both normo- and hypercholesterolaemic animals from 0.028 to 0.042 and 0.034 to 0.047 sarc-1s-1 (normo- and hypercholesterolaemic, respectively; n=14 vs 14 and 7 vs 15). While leaving the full width at half maximum unchanged the drug significantly increased the amplitude of sparks in both groups (0.405±0.005 vs 0.436±0.004 and 0.354±0.004 vs 0.422±0.005; n=605 vs 1429 and 741 vs 1052). This gave rise to an increased amount of released calcium in statin treated animals as reflected in the elevated signal mass.