N-type and P͞Q-type Ca 2؉ channels are inhibited by neurotransmitters acting through G protein-coupled receptors in a membranedelimited pathway involving G␥ subunits. Inhibition is caused by a shift from an easily activated ''willing'' (W) state to a moredifficult-to-activate ''reluctant'' (R) state. This inhibition can be reversed by strong depolarization, resulting in prepulse facilitation, or by protein kinase C (PKC) phosphorylation. Comparison of regulation of N-type Ca 2؉ channels containing Cav2.2a ␣1 subunits and P͞Q-type Ca 2؉ channels containing Cav2.1 ␣1 subunits revealed substantial differences. In the absence of G protein modulation, Ca v 2.1 channels containing Ca v  subunits were tonically in the W state, whereas Cav2.1 channels without  subunits and Cav2.2a channels with  subunits were tonically in the R state. Both Cav2.1 and Ca v2.2a channels could be shifted back toward the W state by strong depolarization or PKC phosphorylation. Our results show that the R state and its modulation by prepulse facilitation, PKC phosphorylation, and Ca v subunits are intrinsic properties of the Ca 2؉ channel itself in the absence of G protein modulation. A common allosteric model of G protein modulation of Ca 2؉ -channel activity incorporating an intrinsic equilibrium between the W and R states of the ␣1 subunits and modulation of that equilibrium by G proteins, Ca v subunits, membrane depolarization, and phosphorylation by PKC accommodates our findings. Such regulation will modulate transmission at synapses that use N-type and P͞Q-type Ca 2؉ channels to initiate neurotransmitter release.neuromodulation ͉ calcium channels ͉ G␥ subunits ͉ protein phosphorylation N euronal voltage-gated Ca 2ϩ channels are involved in multiple cellular functions including neurotranstransmitter release, Ca 2ϩ -mediated regulatory processes, and generation of dendritic action potentials. Electrophysiological and pharmacological studies distinguish at least six classes of Ca 2ϩ currents designated L-, N-, P-, Q-, R-, and T-type (1, 2). Ca 2ϩ channels consist of complexes of a pore-forming ␣ 1 subunit with ␣ 2