An in vivo model for studying the dynamics of intracellular free calcium changes in slow- and fast-twitch muscle fibres

• Published in: Pflügers Archiv Vol. 438; no. 5; pp. 665 - 670
• Main Authors: Bátkai, S, Rácz, I B, Ivanics, T, Tóth, A, Hamar, J, Slaaf, D W, Reneman, R S, Ligeti, L
• Format: Journal Article
• Language: English
• Published: Germany 01.10.1999
• Subjects: Animals; Caffeine - pharmacology; Calcium - metabolism; Cytosol - metabolism; Fluorescent Dyes; Indoles; Male; Models, Biological; Muscle Contraction - drug effects; Muscle Fibers, Fast-Twitch - drug effects; Muscle Fibers, Fast-Twitch - metabolism; Muscle Fibers, Slow-Twitch - drug effects; Muscle Fibers, Slow-Twitch - metabolism; Muscle, Skeletal - metabolism; Muscle, Skeletal - ultrastructure; Rats; Rats, Sprague-Dawley; Space life sciences
• ISSN: 0031-6768; 1432-2013
• DOI: 10.1007/s004240051091

The understanding of the regulation of the free cytosolic [Ca2+] ([Ca2+]i) in skeletal muscle is hampered by the lack of techniques for quantifying free [Ca2+]i in muscle fibres in situ. We describe a model for studying the dynamics of free [Ca2+]i in the fast-twitch extensor digitorum longus (EDL) and the slow-twitch soleus (SOL) muscles of the rat in vivo using caffeine superfusion to induce changes in free [Ca2+]i. We assumed that differences in sensitivity between the two muscle types for this substance reflect differences in intracellular Ca2+ handling in the fibres of which these muscles consist. The Indo-1 ratiometric method, using intravital microscopy with incident light, was adapted to measure free [Ca2+]i in vivo. Fluorescence images were collected by means of a digital camera. Caffeine superfusion at 37 degrees C for 2 min, at concentrations of 1, 2, 5, 10 or 20 mmol/l, induced a concentration-dependent increase in free [Ca2+]i and revealed differences in caffeine sensitivity between the muscle types, with the SOL being more sensitive. In a separate set of experiments the contracture threshold, as assessed by topical application of caffeine, was determined in both muscle types. EDL had a higher threshold for developing contracture than SOL. These finding are in agreement with previous in vitro studies. We may conclude that the dynamics of free [Ca2+]i can be assessed reliably in intact mammalian muscle in vivo.