pH modulates conducting and gating behaviour of single calcium release channels

Intracellular pH changes affect excitation-contraction coupling in skeletal and cardiac muscles. However the proton implication in modulating the sarcoplasmic reticulum Ca2+ release channel activity has never been visualized at single channel level. A large conducting Ca2+ release pathway has previously been characterized after incorporation of skeletal and cardiac sarcoplasmic reticulum vesicles into planar lipid bilayers. This channel has been activated by micromolar and millimolar concentrations of Ca2+ and ATP, respectively. The pH was independently varied on each side of the channels. Acidification of the cis-chamber (7.4 to 6.6) induced a modification of the gating behaviour, resulting in a decrease of the open probability. This effect was completely reversible. On the other hand, acidification of the trans-chamber (7.4 to 6.8) induced a reduction of the unitary conductance of the sarcoplasmic reticulum Ca2+ release channel.