ALPHA-1-ADRENOCEPTOR ACTIVATION POTENTIATES TAURINE RESPONSE MEDIATEDBY PROTEIN-KINASE-C IN SUBSTANTIA-NIGRA NEURONS

1. The potentiation of glycine receptor-mediated taurine response (I-t au) by alpha 1 adrenoceptor activation was investigated in neurons fre shly dissociated from the rat substantia nigra (SN) using a nystatin p erforated-patch recording. 2. Norepinephrine (NE) at a concentration o f 10(-4) M in the presence of 10(-5) M yohimbine and 10(-5) M proprano lol potentiated the peak amplitude of I-tau (10(-3) M) at a holding po tential of -40 mV under voltage clamp conditions. NE could be substitu ted by phenylephrine at this potentiation. 3. This potentiation of the taurine response persisted in the treatment with pertussis toxin (500 ng/ml) for 18 h. The intracellular application of GDP-beta S (100 mu M) with a conventional whole cell patch recording mode abolished the e ffect of alpha 1 adrenoceptor activation on the I-tau. 4. Staurosporin e (10(-7) M) blocked the enhancement of I-tau by 10(-4) M NE with 10(- 5) M yohimbine and 10(-5) M propranolol. In addition, phorbol-12-myris tate 13-acetate (10(-5) M) potentiated I-tau. 5. The intracellular app lication of 0.275 U/ml protein kinase C (PKC) with a conventional whol e cell configuration gradually increased the peak amplitude of I-tau. On the other hand, intracellular perfusion either without PKC or with PKC plus 4 mu M PKC (1936), a PKC inhibitor, did not potentiate I-tau. 6. A single channel recording in a cell attached configuration reveal ed that NE (10(-4) M) with 10(-5) M yohimbine and 10(-5) M propranolol increased the total open time of the taurine-activated channel. This increase of the channel opening was antagonized by staurosporine (10(- 7) M). 7. Neither tapsigargin (10(-6) M), LiCl (10(-4) M), trifluopera zine (10(-5) M) nor (S)-5-isoquinolinesulfonic acid, mino]-3-oxo-(4-ph enyl-1-piperazinyl)-propyl]phenyl ester (10(-4) M) applied in the perf usate were found to affect the potentiation of I-tau by alpha 1 adreno ceptor. The intracellular application of inositol triphosphates (10(-4 ) M) in a conventional whole cell recording also had no effect on I-ta u. 8. These findings thus indicate that alpha 1 adrenoceptor coupled w ith pertussis-insensitive G protein increases the intracellular PKC ac tivity, thus leading to an increase in the channel opening activated b y taurine and an enhancement of the peak amplitude of I-tau in the SN neurons.