Sparse but highly efficient Kv3 outpace BKCa channels in action potential repolarization at hippocampal mossy fiber boutons - PubMed (original) (raw)

BKCa channels do not activate during basal MFB–APs, and their calcium source is remote. A, Focal application of IBTX (1 μ

m

), BDS-I (3 μ

m

) + IBTX, or DTX (0.2 μ

m

) + IBTX to different (diff.) MFBs while recording APs generated by local current injection. Black traces, Baseline; red traces, during drug application. B, Collected data for changes of MFB–AP half-durations (AP-hd) during focal application of IBTX (n = 4), Pax (n = 4), BDS-I + IBTX (n = 3), DTX + IBTX (n = 4), and all three drugs simultaneously (n = 3) (in black), including data from Figure 1_C_ (in gray) for comparison. C, Recordings of locally elicited MFB–APs in ACSF (top) or in ACSF containing 10 μ

m

4-AP (middle and bottom) with 10 m

m

BAPTA (top and middle) or 10 m

m

EGTA (bottom) in the intracellular solution. Black traces represent APs recorded immediately after establishing the whole-cell configuration; red traces represent APs recorded after 6 min in the whole-cell configuration. D, Changes in MFB–AP half-durations after 6 min recording time relative to those determined initially for experiments in ACSF and 10 m

m

BAPTA (left; n = 3), in ACSF containing 10 μ

m

4-AP and intracellularly 10 m

m

BAPTA (middle; n = 4) or 10 m

m

EGTA (right; n = 4). E, Top traces, MFB–AP-wave commands with different half-durations (left, basal MFB–AP; right, AP-hd, ∼700 μs), applied in TTX (1 μ

m

), 4-AP (1 m

m

), and with 0.2 m

m

EGTA in the intracellular recording solution. Both waveforms were applied to an individual MFB. Bottom, Corresponding current traces in control and after focal application of IBTX (1 μ

m

; red traces). Subtracted traces (control-IBTX) shown in green (_I_BKCa, BKCa-mediated current). _I_Cav, Voltage-gated calcium channel-mediated current. Inset shows overlay of both AP waveforms and the BKCa-mediated current in response to the broad AP. Arrow indicates membrane potential of broad AP, at which _I_BKCa sets on. F, Top, Wave command of basal MFB–AP. Bottom, BKCa-mediated current (_I_BKCa, green) recorded in the presence of TTX, Cd2+, and 1 m

m

4-AP, using an intracellular solution containing 0.1 m

m

free Ca2+. Black traces represent recordings from a different MFB in TTX and Cd2+ using an intracellular solution containing 0.2 m

m

EGTA, before (_I_Kv, Kv-mediated current) and after bath application of 1 m

m

4-AP. Arrows indicate respective membrane potentials, at which currents set on.