L-type Ca2+ channel and ryanodine receptor cross-talk in frog skeletal muscle

The dihydropyridine receptors (DHPRs)/L-type Ca2+ channels of skeletal muscle are coupled with ryanodine receptors/Ca2+ release channels (RyRs/CRCs) located in the sarcoplasmic reticulum (SR). The DHPR is the voltage sensor for excitation-contraction (EC) coupling and the charge movement component q(gamma) has been implicated as the signal linking DHPR voltage sensing to Ca2+ release from the coupled RyR. Recently, a new charge component, q(h), has been described and related to L-type Ca2+ channel gating. Evidence has also been provided that the coupled RyR/CRC can modulate DHPR functions via a retrograde signal. Our aim was to investigate whether the newly described q(h) is also involved in the reciprocal interaction or cross-talk between DHPR/L-type Ca2+ channel and RyR/CRC. To this end we interfered with DHPR/L-type Ca2+ channel function using nifedipine and 1-alkanols (heptanol and octanol), and with RyR/CRC function using ryanodine and ruthenium red (RR). Intramembrane charge movement (ICM) and L-type Ca2+ current (I-Ca) were measured in single cut fibres of the frog using the double-Vaseline-gap technique. Our records showed that nifedipine reduced the amount of q(gamma) and q(h) moved by similar to90% and similar to55%, respectively, whereas 1-alkanols completely abolished them. Ryanodine and RR shifted the transition voltages of q(gamma) and q(h) and of the maximal conductance of I-Ca by similar to4-9 mV towards positive potentials. All these interventions spared q(beta). These results support the hypothesis that only q(gamma;) and q(h) arise from the movement of charged particles within the DHPR/L-type Ca2+ channel and that these charge components together with I-Ca are affected by a retrograde signal from RyR/CRC.