I_a Potassium Channels In Rat Cerebellar Granule Cell Apoptosis

Apoptosis or programmed cell death is critical for the normal development and homeostasis of multicellular organisms. Apoptosis regulation has been implicated in many diseases such as cancer, autoimmume, neurodegenerative. Compelling evidence indicates that excessive K+ efflux and intracellular K+ depletion are key early steps in apoptosis. Physiological concentration of intracellular K+ could act as a repressor of apoptotic effectors. In many cell types, a huge loss of cellular K+ may serve as a death signal allowing the execution of the suicide program by activating key events in apoptotic cascade including caspase activation, cytochrome c release, and endonuclease activation. Among the many different types of K+ channels, the outward delayed rectifier channels( Ik) are generally believed to play an impotant role in excessive K+ efflux during apoptosis. But we know little about whether other K+ channels are involved in it. In order to further understand the mechanism of early excessive K+ efflux in apoptosis, we investigate the relationship between IA channels and apoptosis by patch-clamp, RNAi and so on. We used rat cerebellar granule cells apoptosis induced by low K+ without serum as apoptosis model. The research includes three parts, the results as following:Part 1: Low potassium without serum cause the primary cultured cerebellar granule cells ( after 6 days in vitro) apoptosis . The IA currents increased dramaticly (a 27% increase; n=31), and the steady-state activation and inactivatin kinetics of IA also changed significantly at the early step in apoptosis. 2-iodomelatonin, an agonist of melatonin receptor, could cause a reversible decrease the IA current amplitude in all tested cells, and modified the IA channel activation kinetics of control cells. The melatonin receptor antagonist, 4P-PDOT, could not abrogate the effect of 2-iodomelatonin on augentation. This suggested that 2-iodomelatonin was not likely inhibit IA channel via melatonin receptor. 2-iodomelatonin prevented apoptosis of cerebellar granule cells induced by low K+ without serum, and the protective function may be relative to reducing IA current.Part 2: 4-AP, an IA channel selective inhibitor, not only inhibited IA currents, modified it's the steady-state activation and inactivatin kinetics,but also prevented apoptosis of rat cerebellar granule neurons induced by low K+ without serum. 4-AP...