Calcium-induced transitions between the spontaneous miniature outward and the transient outward currents in retinal amacrine cells

The Journal of General Physiology
Pratip Mitra, Malcolm M Slaughter

Abstract

Spontaneous miniature outward currents (SMOCs) occur in a subset of retinal amacrine cells at membrane potentials between -60 and -40 mV. At more depolarized potentials, a transient outward current (I(to)) appears and SMOCs disappear. Both SMOCs and the I(to) are K(+) currents carried by BK channels. They both arise from Ca(2+) influx through high voltage-activated (HVA) Ca(2+) channels, which stimulates release of internal Ca(2+) from caffeine- and ryanodine-sensitive stores. An increase in Ca(2+) influx resulted in an increase in SMOC frequency, but also led to a decline in SMOC mean amplitude. This reduction showed a temporal dependence: the effect being greater in the latter part of a voltage step. Thus, Ca(2+) influx, although required to generate SMOCs, also produced a negative modulation of their amplitudes. Increasing Ca(2+) influx also led to a decline in the first latency to SMOC occurrence. A combination of these effects resulted in the disappearance of SMOCs, along with the concomitant appearance of the I(to) at high levels of Ca(2+) influx. Therefore, low levels of Ca(2+) influx, arising from low levels of activation of the HVA Ca(2+) channels, produce randomly occurring SMOCs within the range of -60 to -40 mV. Fur...Continue Reading

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Citations

Apr 4, 2002·The Journal of General Physiology·Pratip Mitra, Malcolm M Slaughter
Jul 11, 2008·The Journal of Comparative Neurology·Paul WitkovskyDavid Krizaj
Apr 27, 2016·The Journal of Physiology·Jay Garaycochea, Malcolm M Slaughter
May 25, 2006·Journal of Neuroscience Research·Luoxiu Huang, Lei Li
Nov 19, 2005·Journal of Neurophysiology·Ajithkumar WarrierMartin Wilson

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