Aims: 

Trout and mammalian ventricular myocytes are different in form and function. In form, trout myocytes are long and slender and lack t-tubular invaginations of the sarcolemma. In this regard they resemble mammalian atrial and neonatal ventricular myocytes, and ventricular myocytes from all other non-mammalian species. In function, the excitation-contraction coupling of trout myocytes is more dependent on Ca²⁺ -influx across the sarcolemma via L-type Ca²⁺ -channels and reverse-mode Na⁺/Ca²⁺ -exchange (NCX). The importance of Ca²⁺ -induced Ca²⁺ -release from the sarcoplasmic reticulum via ryanodine receptors (RYR) is controversial. The aim of this study was to investigate the cellular localization of the three proteins responsible for Ca²⁺ fluxes: L-type Ca²⁺ -channels, NCX and RYR.

Methods: 

Trout ventricular myocytes were co-labelled with phalloidin to visualize actin and specific antibodies against L-type Ca²⁺ -channels, NCX or RYR. Cells were imaged by confocal microscopy or widefield microscopy followed by deconvolution.

Results: 

Our results suggest that L-type Ca²⁺ -channels, NCX and RYR are organized in distinct, parallel bands on or near the sarcolemma. Bands of L-type Ca²⁺ -channels seemed to align with the Z-line of the sarcomeres. Bands of NCX were located between Z-lines. Bands of RYR seem to align with the M-band in the middle of the sarcomeres.

Conclusion: 

This is the first study to look at the cellular organization of L-type Ca²⁺ -channels, NCX and RYR relative to the sarcomeres. Surprisingly, in trout myocytes L-type Ca²⁺ -channels and RYR did not seem to be co-localized as they are in mammalian myocytes. The functional importance of this will be discussed.