MODULATION OF THE CLONED SKELETAL-MUSCLE L-TYPE CA2-DEPENDENT PROTEIN-KINASE( CHANNEL BY ANCHORED CAMP)

Ca2+ influx through skeletal muscle Ca2+ channels and the force of con traction are increased in response to p-adrenergic stimulation and hig h-frequency electrical stimulation. These effects are thought to be me diated by cAMP-dependent phosphorylation of the skeletal muscle Ca2+ c hannel, Modulation of the cloned skeletal muscle Ca2+ channel by cAMP- dependent phosphorylation and by depolarizing prepulses was reconstitu ted by transient expression in tsA-201 cells and compared to modulatio n of the native skeletal muscle Ca2+ channel as expressed in mouse 129 CB3 skeletal muscle cells. The heterologously expressed Ca2+ channel c onsisting of alpha(1), alpha(2) delta, and beta subunits gave currents that were similar in time course, current density, and dihydropyridin e sensitivity to the native Ca2+ channel. cAMP-dependent protein kinas e (PKA) stimulation by Sp-5,6-DCI-cBIMPS (cBIMPS) increased currents t hrough both native and expressed channels two- to fourfold. Tail curre nts after depolarizations to potentials between -20 and +80 mV increas ed in amplitude and decayed more slowly as either the duration or pote ntial of the depolarization was increased. The time- and voltage-depen dent slowing of channel deactivation required the activity of PKA, bec ause it was enhanced by cBIMPS and reduced or eliminated by the peptid e PKA inhibitor PKI (5-24) amide. This voltage-dependent modulation of the cloned skeletal muscle Ca2+ channel by PKA also required anchorin g of PKA by A-Kinase Anchoring Proteins because it was blocked by pept ide Ht 31, which disrupts such anchoring. The results show that the sk eletal muscle Ca2+ channel expressed in heterologous cells is modulate d by PKA at rest and during depolarization and that this modulation re quires anchored protein kinase, as it does in native skeletal muscle c ells.