Norepinephrine-induced Ca2+ current inhibition in adult rat sympathetic neurons does not require protein kinase C...

Experiments were performed to investigate if protein kinase C is involved in the norepinephrine-induced alpha 2-adrenoceptor-mediated inhibition of the Ca2+ current in adult rat superior cervical ganglion neurons. Ca2+ currents were recorded from dispersed superior cervical ganglion neurons, acutely isolated from adult rats, using the whole-cell patch-clamp technique. Both norepinephrine and the protein kinase C activator, 1,2-dioctanoylglycerol (diC8) decreased the Ca2+ current induced by step depolarizations to +10 mV from a holding potential of -80 mV. In the presence of norepinephrine, the Ca2+ current rising phase was adequately fit by a double exponential with a second time constant much larger than control, whereas in the presence of diC8 the rising phase became mono-exponential and the current displayed a prominent decay. Control tail current activation curves were described by the sum of two Boltzmann functions. Both norepinephrine and diC8 reduced peak tail current amplitude. Norepinephrine preferentially reduced the component activated at more hyperpolarized potentials, while diC8 preferentially reduced the component activated at more depolarized potentials. Intracellular application of three protein kinase C inhibitors: protein kinase C pseudosubstrate (PKC-19-36) (2 microM), staurosporine (1 microM) and 1-(5-isoquinolinylsulonyl)-2-sulfonylpiperazine (H-7) (50 microM), failed to affect norepinephrine-induced Ca2+ current inhibition. In addition, these protein kinase C inhibitors did not decrease the Ca2+ current inhibition induced by diC8.(ABSTRACT TRUNCATED AT 250 WORDS)