Calcium-activated potassium channels in resting and activated human T lymphocytes. Expression levels, calcium dependence, ion selectivity, and pharmacology.

Abstract

Ca2+-activated K+[K(Ca)] channels in resting and activated human peripheral blood T lymphocytes were characterized using simultaneous patch-clamp recording and fura-2 monitoring of cytosolic Ca 2+ concentration, [Ca2+]i . Whole-cell experiments, using EGTA-buffered pipette solutions to raise [CaZ÷]i to 1 p,M, revealed a 25-fold increase in the number of conducting K(Ca) channels per cell, from an average of 20 in resting T cells to > 500 channels per cell in T cell blasts after mitogenic activation. The opening of K(Ca) channels in both whole-cell and inside-out patch experiments was highly sensitive to [Ca2+]i (Hill coefficient of 4, with a midpoint of ~ 300 nM). At optimal [Ca2+]i, the open probability of a K(Ca) channel was 0.3-0.5. K(Ca) channels showed little or no voltage dependence from -100 to 0 inV. Single-channel/-V curves were linear with a unitary conductance of 11 pS in normal Ringer and exhibited modest inward rectification with a unitary conductance of ~35 pS in symmetrical 160 mM K ÷. Permeability ratios, relative to K +, determined from reversal potential measurements were: K + (1.0) > Rb + (0.96) > NH~" (0.17) > Cs ÷ (0.07). Slope conductance ratios were: NH~ (1.2) > K + (1.0) > Rb + (0.6) > Cs ÷ (0.10). Extracellular Cs + or Ba 2+ each induced voltagedependent block of K(Ca) channels, with block increasing at hyperpolarizing potentials in a manner suggesting a site of block 75% across the membrane field from the outside. K(Ca) channels were blocked by tetraethylammonium (TEA) applied externally (Kd = 40 mM), but were unaffected by 10 mM TEA applied inside by pipette perfusion. K(Ca) channels were blocked by charybdotoxin (CTX) with a half-blocking dose of 3-4 nM, but were resistant to block by noxiustoxin (NTX) at 1-100 nM. Unlike K(Ca) channels in Jurkat T cells, the K(Ca) channels of normal resting or activated T cells were not blocked by apamin. We conclude that while K(Ca) and voltage-gated K + channels in the same cells share similarities in ion

ADP and inositol trisphosphate evoke oscillations of a monovalent cation conductance in rat megakaryocytes

“…2A, thus to selectively record these events prior to their run-down, K¤ currents were further inhibited by addition of CTX to the external saline. Two main classes of K¤ channel exist in megakaryocytes, voltage-gated K¤ channels (KV) and intermediate conductance Ca¥-gated K¤ channels (IKCa) (Kawa, 1990;Uneyama et al 1993a (Sands et al 1989;Grissmer et al 1993). In this study we added 100 nÒ recombinant CTX to the bath to block both classes of K¤ current.…”

Mechanisms underlying the cardiac pacemaker: the role of SK4 calcium-activated potassium channels

“…In the periphery, the SK channels are expressed in T-lymphocytes and atrial cells and play an important role in atrial repolarization [143][144][145][146][147][148] . SK1 channels are resistant to apamin [136] , and their unitary conductance varies from 11 to 26 pS depending on the experimental conditions [149][150][151] . They can associate with SK2 to form heterotetrameric channels.…”

Functional Blockade of the Voltage-gated Potassium Channel Kv1.3 Mediates Reversion of T Effector to Central Memory Lymphocytes through SMAD3/p21cip1 Signaling

“…In G2/M the cell membrane becomes depolarized and K ϩ flux is decreased, with a corresponding increase in Cl channel conductance (9). In addition to the long recognized role of ion channels in cellular proliferation, the reverse is also true, as mitogens have been shown to up-regulate potassium channels including Kv1.3 (10,11).…”