The Effect of Activation of Protein Kinase C on the Calcium-dependent K; Current in Rat Basilar Smooth Muscle Cells

OBJECTIVE: Activation of protein kinase C(PKC) may play a certain role in the development of cerebral vasospasm. However, this mechanism still elusive. This study was undertaken to investigate the action of protein kinase C on calcium-dependent K+ channels(KCa) and internal calcium concentration [Ca2+]i in freshly isolated smooth muscle cells. METHODS: Whole-cell patch clamp and calcium microfluorimetry technique were used for measuring the K Ca and internal calcium concentration. RESULTS: In patch-clamp studies, depolarization evoked an outward KCa current which is sensitive to caffeine and A23187, and shown to be blocked by TEA(tetraethylammonium) but not by glibenclamide. Activation of protein kinase C by phorbol 12-myristate 13-acetate(PMA:1-100nmol/1) and phorbol 12, 13-dibutyrate(PDB:1-100nmol/1) dose-dependently enhanced KCa current. Subsequent application of TEA(10-30mmol/1) but not glibenclamide(3-6nmol/1), in the presence of phorbol esters, reduced the potassium current activated by phorbol esters. Preincubation with 1-(5-isoquinoline sulphonyl)-2-methylpiperazine(H-7:10nmol/1), a protein kinase C inhibitor, prevented the effect of phorbol esters on KCa. In calcium microfluorimetric studies, PMA(100nmol/1) increased intracellular calcium concentration and this effect of PMA was prevented by pre-incubation of cells with H-7(10nmol/1). CONCLUSION: These results indicate that activation of PKC increases intracellular calcium concentration and elevation of internal calcium concentration activates KCa in cerebral vascular smooth muscle cells.

Effect of PNS on post hyperpolarization potential in rat stellate ganglion neurons / 中国药理学通报

Aim To study the relationship between theeffects of saponins of panax notoginseng(PNS)on fir-ing frequency and hyperpolarization potential in neu-rons.Methods Applieation of a depolarizing currentpulse to stellate ganglion(SG) neurons of rat evokedaction potentials(AP).These neurons were classifiedas phasic or tonic neurons on the basis of their firingpatterns.Then we investigated the effects of PNS on fir-ing pattern and frequency,after hyperpolarization po-tential(AHP) and fastexcitatory postsynaptic potential(f-EPSP) in high Ca2 +Krebs’solution of SG neuronsin rat.Results The firing frequency of tonic neuronswas reduced by PNS.At the concentration of0.12 ~0.16 g.L-1,PNS reversibly depressed AHP in a dosedependentmanner.And the aggrandizing action of highCa2 +on f-EPSP was antagonized by PNS.Conclusion PNS can reduce the firing frequency of rat SG neu-rons,but this action was not caused by reinforcement ofAHP potential.The restraining regulation of excitabili-ty of neurons by PNS may underlie its inhibitory actionon calcium influx.