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This Article Full Text Full Text (PDF) All Versions of this Article: 555/1/137    most recent jphysiol.2003.051730v1 Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via Google Scholar Google Scholar Articles by Squecco, R. Articles by Francini, F. Search for Related Content PubMed PubMed Citation Articles by Squecco, R. Articles by Francini, F.

Department of Physiological Sciences, University of Florence, Viale GB Morgagni 63, I-50134 Firenze, Italy

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 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 and q_h moved by 90% and 55%, respectively, whereas 1-alkanols completely abolished them. Ryanodine and RR shifted the transition voltages of q and q_h and of the maximal conductance of I_Ca by 4-9 mV towards positive potentials. All these interventions spared q_ß. These results support the hypothesis that only q_; 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.

(Received 16 September 2003; accepted after revision 5 December 2003; first published online 5 December 2003)
Corresponding author F. Francini: Department of Physiological Sciences, University of Florence, Viale G.B. Morgagni, 63, 50134 Florence, Italy.  Email: fabio.francini{at}unifi.it