During patch-clamp recordings from fish retinal ganglion cells, excess depolarization by inward current passage across uncompensated series resistance can give rise to the appearance of fast and tetrodotoxin-blockable outward K`+current activation (Pignatelli & Ishida Soc. Neurosci.Abstr. 24: 1026, 1998). This fast outward current component was detected during recordings without series resistance compensation, but not it 80% series resistance compensation was applied. Also, we noted that this outward current increased in amplitude at rates resembling those of previously reported Na+-activated K+ currents. Because previous voltage-clamp studies suggested that Na+activated K+ current contributes to spike repolarization in neurons, we calculated membrane potential changes produced by depolarizing current injections into cells modelled by measured values of voltage-gated Na+ and K+ conductances. leak conductance, and whole-cell capacitance. When outward current activation rate was set as fast as that of the tetrodotoxin•sensitive outward component, repetitive spikes were not elicited at any stimulus current intensity, and spikes that overshoot zero rnV could not be generated. If, instead, these calculations incorporated K+ current activation rates measured with 80% series resistance compensation, current injections of 8-100 pA elicited repetitive spiking at frequencies (10- 85 Hz) resembling those recorded from ganglion cells in various preparations. Our calculations imply that whole-cell outward K+ current activation rates recorded without series resistance compensation are inordinately rapid, and that Na+-activated K+ currents are unlikely to repolarize single spikes. Supported by NIH Grant ttE‘/08120
FAST OUTWARD CURRENT RATE PRECLUDES REPETITNE SPIKING IN RETINAL GANGLION CELLS.
PIGNATELLI, Angela;
1999
Abstract
During patch-clamp recordings from fish retinal ganglion cells, excess depolarization by inward current passage across uncompensated series resistance can give rise to the appearance of fast and tetrodotoxin-blockable outward K`+current activation (Pignatelli & Ishida Soc. Neurosci.Abstr. 24: 1026, 1998). This fast outward current component was detected during recordings without series resistance compensation, but not it 80% series resistance compensation was applied. Also, we noted that this outward current increased in amplitude at rates resembling those of previously reported Na+-activated K+ currents. Because previous voltage-clamp studies suggested that Na+activated K+ current contributes to spike repolarization in neurons, we calculated membrane potential changes produced by depolarizing current injections into cells modelled by measured values of voltage-gated Na+ and K+ conductances. leak conductance, and whole-cell capacitance. When outward current activation rate was set as fast as that of the tetrodotoxin•sensitive outward component, repetitive spikes were not elicited at any stimulus current intensity, and spikes that overshoot zero rnV could not be generated. If, instead, these calculations incorporated K+ current activation rates measured with 80% series resistance compensation, current injections of 8-100 pA elicited repetitive spiking at frequencies (10- 85 Hz) resembling those recorded from ganglion cells in various preparations. Our calculations imply that whole-cell outward K+ current activation rates recorded without series resistance compensation are inordinately rapid, and that Na+-activated K+ currents are unlikely to repolarize single spikes. Supported by NIH Grant ttE‘/08120I documenti in SFERA sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
