Physiological Properties of Zebrafish Embryonic Red and White Muscle Fibers During Early Development

Abstract

The zebrafish is a model organism for studies of vertebrate muscle differentiation and development. However, an understanding of fish muscle physiology during this period is limited. We examined the membrane, contractile, electrical coupling, and synaptic properties of embryonic red (ER) and white (EW) muscle fibers in developing zebrafish from 1 to 5 days postfertilization. Resting membrane potentials were -73 mV in 1 day ER and -78 mV in 1 day EW muscle and depolarized 17 and 7 mV, respectively, by 5 days. Neither fiber type exhibited action potentials. Current-voltage relationships were linear in EW fibers and day 1 ER fibers but were outwardly rectifying in some ER fibers at 3 to 5 days. Both ER and EW fibers were contractile at all ages examined (1 to 5 days) and could follow trains of electrical stimulation of up to 30 Hz without fatiguing for up to 5 min. Synaptic activity consisting of miniature endplate potentials (mEPPs) was observed at the earliest ages examined (1.2-1. 4 days) in both ER and EW fibers. Synaptic activity increased in frequency, and mEPP amplitudes were larger by 5 days. Miniature EPP rise times and half-widths decreased in ER fibers by 5 days, while EW fiber mEPPs showed fast kinetics as early as 1.2-1.4 days. ER and EW muscle fibers showed extensive dye coupling but not heterologous (red-white) coupling. Dye coupling decreased by 3 days yet remained at 5 days. Somites were electrically coupling, and this allowed filtered synaptic potentials to spread from myotome to myotome. It is concluded that at early developmental stages the physiological properties of ER and EW muscle are similar but not identical and are optimized to the patterns of swimming observed at these stages.

Activation of Embryonic Red and White Muscle Fibers During Fictive Swimming in the Developing Zebrafish

“…1-4). However, the time course of larval ER and EW muscle miniature EPPs are similar (Buss and Drapeau 2000;Nguyen et al 1999), indicating that the rhythmic EPP summation was likely due to other factors. EPP summation could be due to EPPs originating from adjacent electrically coupled ER muscle fibers as EW fiber coupling is minimal at day 3, whereas ER fibers are extensively coupled (Buss and Drapeau 2000).…”

“…All procedures were carried out in compliance with the guidelines stipulated by the Canadian Council for Animal Care and McGill University. The experimental methodology has been described (Buss and Drapeau 2000). Results are taken from 25 paired and 28 single whole-cell patch-clamp recordings from ER and EW muscle fibers of zebrafish embryos aged 1.3-1.6 (day 1, length approximately 2.5 mm) and larvae aged 3.0 -3.3 (day 3, length approximately 3.5 mm) days postfertilization.…”

“…Analyses were performed using pClamp 8 software (Axon Instruments). ER fibers were distinguished by their superficial distribution and longitudinal orientation, whereas EW fibers were deeper and had an oblique orientation (Buss and Drapeau 2000). Measurements of fictive swimming and coiling duration, rhythmic end plate potential (EPP) frequency, and rostral-caudal delay were made by eye (cursor measurement).…”

“…EPP summation could be due to EPPs originating from adjacent electrically coupled ER muscle fibers as EW fiber coupling is minimal at day 3, whereas ER fibers are extensively coupled (Buss and Drapeau 2000). To test whether the summation of rhythmic EPPs in ER but not EW fibers was due to electrical coupling, recordings were made from day 1 ER and EW muscle fibers which are both extensively electrically coupled at this age (Buss and Drapeau 2000).…”

Amino acid variations resulting in functional and nonfunctional zebrafish P2X1 and P2X5.1 receptors

“…Electrophysiological recordings were obtained from axial skeletal muscle as previously described [10]. In brief, embryos and larvae were anesthetized in 1× Evans recording solution (in mM): 134 NaCl, 2.9 KCl, 2.1 CaCl 2 , 1.2 MgCl 2 , 10 glucose, 10 HEPES, pH 7.8, containing 0.02% tricaine and pinned to a 35-mm dish coated with Sylgard through the notochord using 25 μm tungsten wires.…”