Cortisol inhibition of calcium currents in guinea pig hippocampal CA1 neurons via G-protein-coupled activation of protein kinase C.
The inhibition of voltage-activated Ca2+ channel currents by cortisol (hydrocortisone), the principal glucocorticoid in man and guinea pig, was examined in freshly dissociated pyramidal neurons from the adult guinea pig hippocampal CA1 region using whole-cell voltage-clamp recordings. Steady-state inhibition by cortisol of the peak Ca2+ channel current evoked by depolarization from -80 to -10 mV increased in a concentration-dependent fashion, with a maximal inhibition of 63 +/- 4% of the total current at 100 microM. Cortisone had a maximal 17 +/- 2% inhibition at 10 microM. Corticosterone and the metabolite allotetrahydrodeoxycorticosterone exhibited a plateau of inhibition of around 15% and 25%, respectively, between 10 pM and 100 nM; both compounds continued to inhibit at concentrations > 10(-7) M. Analysis of tail currents at -80 mV showed that cortisol and corticosterone had no effect on the voltage-dependent activation or deactivation of the Ca2+ channel current. However, cortisol slowed the activation of the current. Cortisol inhibited both the N-type or omega-conotoxin (CgTX)-sensitive, and the L-type or nifedipine (NIF)-sensitive Ca2+ channel current but had no effect on the CgTX/NIF-insensitive Ca2+ channel current. In neurons isolated from pertussis toxin (PTX)-treated animals, the cortisol inhibition was significantly diminished. Intracellular dialysis with GDP-beta-S (500 microM) or with the specific inhibitors of protein kinase C (PKC), the pseudosubstrate PKC inhibitor (PKCI 19-31) (2 microM) and bisindolylmaleimide (BIS) (1 microM) significantly diminished the cortisol inhibition of the Ca2+ channel current. The specific inhibitor of cAMP-dependent protein kinase (PKA) inhibitor, Rp-cAMPS (100 microM) had no effect.(ABSTRACT TRUNCATED AT 250 WORDS)
ffrench-Mullen
J M
JM
Department of Pharmacology, Zeneca Inc., Wilmington, Delaware 19897.
D000818:Animals; D002118:Calcium / Q000502:physiology*; D002121:Calcium Channel Blockers / Q000494:pharmacology*; D004553:Electric Conductivity; D004789:Enzyme Activation; D019204:GTP-Binding Proteins / Q000502:physiology*; D006168:Guinea Pigs; D006624:Hippocampus / Q000166:cytology / Q000502:physiology*; D006854:Hydrocortisone / Q000494:pharmacology*; D007700:Kinetics; D009474:Neurons / Q000502:physiology*; D011493:Protein Kinase C / Q000378:metabolism*
D002121:Calcium Channel Blockers; D011493:Protein Kinase C; D019204:GTP-Binding Proteins; D002118:Calcium; D006854:Hydrocortisone