A. Fleig et R. Penner, SILENT CALCIUM CHANNELS GENERATE EXCESSIVE TAIL CURRENTS AND FACILITATION OF CALCIUM CURRENTS IN RAT SKELETAL MYOBALLS, Journal of physiology, 494(1), 1996, pp. 141-153
1. Whole-cell patch-clamp recordings were employed to study facilitati
on of Ca2+ currents and excessive Ca2+ tail currents evoked by strong
and long-lasting conditioning depolarizations in skeletal myoballs cul
tured from newborn rats.2. Paired-pulse facilitation and excessive tai
l currents showed tile same voltage dependence, becoming prominent at
conditioning potentials above +30 mV. 3. Recruitment of excessive tail
currents and facilitation occurred with the same time dependence (tim
e constant (tau), similar to 200 ms to similar to 1 s) accelerating wi
th tie depolarization strength of conditioning pulses. 4. Reversal of
Ca2+ current facilitation during the repolarization period between con
ditioning and test pulses was time- and voltage dependent. The time wi
ndow of recruitment of facilitated Ca2+ currents narrowed considerably
at more negative repolarization potentials (tau: similar to 10 ms at
-100 mV, but similar to 1.5 s at 0 mV). 5. Neither omission of interna
l ATP nor perfusion of the cells with the peptide inhibitor of protein
kinase A (PKI) had significant effects on Ca2+ current facilitation,
although internal perfusion with ATP gamma S slowly suppressed the fac
ilitation currents by about 30%. External application of either ryanod
ine or caffeine under control conditions selectively and significantly
suppressed the facilitated Ca2+ currents by about 30-40 %. 6. We prop
ose that facilitation of Ca2+ currents and excessive tail currents are
consequences of a common mechanism linked to ryanodine receptors.