Sustained GABA-induced regulation of the inactivation of the voltage-dependent Ca2+ current in crustacean muscle fibers.
We describe a new form of gamma-aminobutyric acid (GABA) -mediated regulation of the inactivation and of the recovery from inactivation of the L-type Ca2+ current (I(Ca)) in crayfish muscle. GABA (1 mM) was applied during a 2-min period and the peak I(Ca) was measured using two-electrode voltage-clamp recordings 30 min after returning to the control solution. Prepulse-pulse protocols showed that the GABA-mediated inhibition of I(Ca) decreased (>50%) both with increasing prepulse depolarization and as the delay between prepulse and pulse was reduced. GABA also shifted to depolarized values (>5 mV) the S-shaped plots of the peak I(Ca) evoked by a constant depolarizing pulse as a function of prepulse voltage (i.e., inactivation curves) and accelerated the recovery time from the inactivation evoked by depolarizing prepulses (>35%). The effects outlasted GABA application up to 1 h. The observed changes in inactivation properties may be of functional importance because they indicate that previous depolarization relieves the GABA-induced inhibition of I(Ca), implying that this long-lasting inhibition is under the regulation of the prepulse potential and the subsequent Ca2+ entry.
Castellote
J M
JM
Instituto Cajal, CSIC, Madrid, Spain.
Buño
W
W
D000818:Animals; D003400:Astacoidea; D002118:Calcium / Q000378:metabolism; D015220:Calcium Channels / Q000502:physiology*; D015640:Ion Channel Gating / Q000187:drug effects / Q000502:physiology*; D008564:Membrane Potentials / Q000187:drug effects / Q000502:physiology; D018485:Muscle Fibers, Skeletal / Q000187:drug effects / Q000502:physiology*; D009433:Neural Inhibition / Q000187:drug effects / Q000502:physiology; D005680:gamma-Aminobutyric Acid / Q000494:pharmacology*
D015220:Calcium Channels; D005680:gamma-Aminobutyric Acid; D002118:Calcium