{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2025,10,8]],"date-time":"2025-10-08T15:14:09Z","timestamp":1759936449909},"reference-count":34,"publisher":"American Physiological Society","issue":"5","content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["Journal of Neurophysiology"],"published-print":{"date-parts":[[1997,11,1]]},"abstract":"<jats:p> Locke, Rachel E. and Jeanne M. Nerbonne. Three kinetically distinct Ca<jats:sup>2+<\/jats:sup>-independent depolarization-activated K<jats:sup>+<\/jats:sup> currents in callosal-projecting rat visual cortical neurons. J. Neurophysiol. 78: 2309\u20132320, 1997. Whole cell, Ca<jats:sup>2+<\/jats:sup>-independent, depolarization-activated K<jats:sup>+<\/jats:sup> currents were characterized in identified callosal-projecting (CP) neurons isolated from postnatal day 7\u201316 rat primary visual cortex. CP neurons were identified in vitro after in vivo retrograde labeling with fluorescently tagged latex microbeads. During brief (160-ms) depolarizing voltage steps to potentials between \u221250 and +60 mV, outward K<jats:sup>+<\/jats:sup> currents in these cells activate rapidly and inactivate to varying degrees. Three distinct K<jats:sup>+<\/jats:sup> currents were separated based on differential sensitivity to 4-aminopyridine (4-AP); these are referred to here as I <jats:sub>A<\/jats:sub>, I <jats:sub>D<\/jats:sub>, and I <jats:sub>K<\/jats:sub>, because their properties are similar (but not identical) K<jats:sup>+<\/jats:sup> currents termed I <jats:sub>A<\/jats:sub>, I <jats:sub>D<\/jats:sub>, and I <jats:sub>K<\/jats:sub> in other cells. The current sensitive to high (\u2265100 \u03bcM) concentrations of 4-AP ( I <jats:sub>A<\/jats:sub>) activates and inactivates rapidly; the current blocked completely by low (\u226450 \u03bcM) 4-AP ( I <jats:sub>D<\/jats:sub>) activates rapidly and inactivates slowly. A slowly activating, slowly inactivating current ( I <jats:sub>K<\/jats:sub>) remains in the presence of 5 mM 4-AP. I <jats:sub>A<\/jats:sub>, I <jats:sub>D<\/jats:sub>, and I <jats:sub>K<\/jats:sub> also were separated and characterized in experiments that did not rely on the use of 4-AP. All CP cells express all three K<jats:sup>+<\/jats:sup> current types, although the relative densities of I <jats:sub>A<\/jats:sub>, I <jats:sub>D<\/jats:sub>, and I <jats:sub>K<\/jats:sub> vary among cells. The experiments here also have revealed that I <jats:sub>A<\/jats:sub>, I <jats:sub>D<\/jats:sub>, and I <jats:sub>K<\/jats:sub> display similar voltage dependences of activation and steady state inactivation, whereas the kinetic properties of the currents are distinct. At +30 mV, for example, mean \u00b1 SD activation \u03c4s are 0.83 \u00b1 0.24 ms for I <jats:sub>A<\/jats:sub>, 1.74 \u00b1 0.49 ms for I <jats:sub>D<\/jats:sub>, and 14.7 \u00b1 4.0 ms for I <jats:sub>K<\/jats:sub>. Mean \u00b1 SD inactivation \u03c4s for I <jats:sub>A<\/jats:sub> and I <jats:sub>D<\/jats:sub> are 26 \u00b1 7 ms and 569 \u00b1 143 ms, respectively. Inactivation of I <jats:sub>K<\/jats:sub> is biexponential with mean \u00b1 SD inactivation time constants of 475 \u00b1 232 ms and 3,128 \u00b1 1,328 ms; \u223c20% of the 4-AP\u2013insensitive current is noninactivating. For all three components, activation is voltage dependent, increasing with increasing depolarization, whereas inactivation is voltage independent. Both I <jats:sub>A<\/jats:sub> and I <jats:sub>K<\/jats:sub> recover rapidly from steady state inactivation with mean \u00b1 SD recovery time constants of 38 \u00b1 7 ms and 79 \u00b1 26 ms, respectively; I <jats:sub>D<\/jats:sub> recovers an order of magnitude more slowly (588 \u00b1 274 ms). The properties of I <jats:sub>A<\/jats:sub>, I <jats:sub>D<\/jats:sub>, and I <jats:sub>K<\/jats:sub> in CP neurons are compared with those of similar currents described previously in other mammalian central neurons and, in the accompanying paper, the roles of these conductances in regulating the firing properties of CP neurons are explored. <\/jats:p>","DOI":"10.1152\/jn.1997.78.5.2309","type":"journal-article","created":{"date-parts":[[2017,12,25]],"date-time":"2017-12-25T01:14:15Z","timestamp":1514164455000},"page":"2309-2320","source":"Crossref","is-referenced-by-count":35,"title":["Three Kinetically Distinct Ca<sup>2+<\/sup>-Independent Depolarization-Activated K<sup>+<\/sup> Currents in Callosal-Projecting Rat Visual Cortical Neurons"],"prefix":"10.1152","volume":"78","author":[{"given":"Rachel E.","family":"Locke","sequence":"first","affiliation":[{"name":"Department of Molecular Biology and Pharmacology, Washington University School of Medicine, St. Louis, Missouri 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