pH modulation of large conductance potassium channel from adrenal chromaffin granules (original) (raw)
Related papers
Calcium-independent K+-selective channel from chromaffin granule membranes
The Journal of Membrane Biology, 1992
Intact adrenal chromaffin granules and purified granule membrane ghosts were allowed to fuse with acidic phospholipid planar bilayer membranes in the presence of Ca 2+ (1 raM). From both preparations, we were able to detect a large conductance potassium channel (ca. 160 pS in symmetrical 400 mM K+), which was highly selective for K + over Na + (PK/PNa = 11) as estimated from the reversal potential of the channel current. Channel activity was unaffected by charybdotoxin, a blocker of the [Ca2+]activated K + channel of large conductance. Furthermore, this channel proved quite different from the previously described channels from other types of secretory vesicle preparations, not only in its selectivity and conductance, but also in its insensitivity to both calcium and potential across the bilayer. We conclude that the chromaffin granule membrane contains a K+-selective channel with large conductance. We suggest that the role of this channel may include ion movement during granule assembly or recycling, and do not rule out events leading to exocytosis.
Small-conductance Ca2+-activated K+ channels in bovine chromaffin cells
Pfl�gers Archiv European Journal of Physiology, 1993
Simultaneous whole-cell patch-clamp and fura-2 fluorescence [Ca2+]~ measurements were used to characterize Ca2+-activated K + currents in cultured bovine chromaffin cells. Extracellular application of histamine (10 gM) induced a rise of [Ca2+]~ concomitantly with an outward current at holding potentials positive to -80 mV. The activation of the current reflected an increase in conductance, which did not depend on membrane potential in the range -80 mV to -40 mV. Increasing the extracellular K + concentration to 20 mM at the holding potential of -78 mV was associated with inwardly directed currents during the [Ca2+]i elevations induced either by histamine (10 gM) or short voltageclamp depolarizations. The current reversal potential was close to the K + equilibrium potential, being a function of external K + concentration. Current fluctuation analysis suggested a unit conductance of 3-5 pS for the channel that underlies this K + current. The current could be blocked by apamin (1 ~tM). Whole-cell current-clamp recordings showed that histamine (10 txM) application caused a transient hyperpolarization, which evolved in parallel with the [Ca2+]~ changes. It is proposed that a small-conductance Ca2+-activated K + channel is present in the membrane of bovine chromaffin cells and may be involved in regulating catecholamine secretion by the adrenal glands of various species.
1995
The properties of Ca2+- and voltage-dependent K+ currents and their role in defining membrane potential were studied in cultured rat chromaffin cells. Two variants of large-con- ductance, Ca2+ and voltage-dependent BK channels, one noninactivating and one inactivating, were largely segre- gated among patches. Whole-cell noninactivating and in- activating currents resulting from each of these channels were segregated among different chromaffin
The heterogeneity of ion channels in chromaffin granule membranes
Cellular & Molecular Biology Letters, 2006
Chromaffin granules are involved in catecholamine synthesis and traffic in the adrenal glands. The transporting membrane proteins of chromaffin granules play an important role in the ion homeostasis of these organelles. In this study, we characterized components of the electrogenic 86Rb+ flux observed in isolated chromaffin granules. In order to study single channel activity, chromaffin granules from the bovine adrenal medulla were incorporated into planar lipid bilayers. Four types of cationic channel were found, each with a different conductance. The unitary conductances of the potassium channels are 360 ± 10 pS, 220 ± 8 pS, 152 ± 8 pS and 13 ± 3 pS in a gradient of 450/150 mM KCl, pH 7.0. A multiconductance potassium channel with a conductivity of 110 ± 8 pS and 31 ± 4 pS was also found. With the exception of the 13 pS conductance channel, all are activated by depolarizing voltages. One type of chloride channel was also found. It has a unitary conductance of about 250 pS in a gra...
The Journal of neuroscience : the official journal of the Society for Neuroscience, 1995
The properties of Ca(2+)- and voltage-dependent K+ currents and their role in defining membrane potential were studied in cultured rat chromaffin cells. Two variants of large-conductance, Ca2+ and voltage-dependent BK channels, one noninactivating and one inactivating, were largely segregated among patches. Whole-cell noninactivating and inactivating currents resulting from each of these channels were segregated among different chromaffin cells. Cell-to-cell variation in the rate and extent of whole-cell current decay was not explained by differences in cytosolic [Ca2+] regulation among cells; rather, variation was due to differences in the intrinsic properties of the underlying BK channels. About 75% of rat chromaffin cells and patches express inactivating BK current (termed BKi) while the remainder express noninactivating BK current (termed BKs). The activation time course of both currents is similar, as is the dependence of activation on [Ca2+] and membrane potential. However, de...
Two components of calcium-activated potassium current in rat adrenal chromaffin cells
The Journal of Physiology, 1992
1. The activation of calcium (Ca2")-dependent potassium (K+) currents in dissociated rat adrenal chromaffin cells was investigated using the dialysed cell recording technique. 2. Ca2+-dependent K+ current was the major component of outward current at command potentials from-30 mV to about + 50 mV. 3. Two components of Ca2+-dependent outward current could be distinguished based on the voltage dependence of activation, the properties of tail currents following repolarization, and pharmacological properties. 4. One Ca2+-dependent current was similar to an after-hyperpolarization current (often termed IAHP) observed in other cell types. This current was largely blocked by 200 nM-apamin or 200 #uM-curare, was associated with slow Ca2+-dependent tail current, and exhibited little dependence on voltage. In cells with cytosolic Ca2+ buffered to 500 nM-1 /Im, curare-sensitive current accounted for most of the membrane current at potentials negative to about-40 mV. 5. A second component of Ca2+-activated K+ current exhibited voltage-dependent activation, was completely blocked by 1 mm-TEA, and turned off rapidly following repolarization. An unusual aspect of the TEA-sensitive currents was that they appeared to inactivate under conditions of constant cytosolic Ca2. 6. A novel observation during these experiments was a slow hump of outward current which appears to result from a non-monotonic elevation in cytosolic Ca2+ during prolonged voltage jumps.
Bovine versus rat adrenal chromaffin cells: big differences in BK potassium channel properties
Journal of neurophysiology, 2000
Both bovine and rat adrenal chromaffin cells have served as pioneering model systems in cellular neurophysiology, including in the study of large conductance calcium- and voltage-dependent K(+) (BK) channels. We now report that while BK channels dominate the outward current profile of both species, specific gating properties vary widely across cell populations, and the distributions of these properties differ dramatically between species. Although BK channels were first described in bovine chromaffin cells, rapidly inactivating ones were discovered in rat chromaffin cells. We report that bovine cells can also exhibit inactivating BK channels with varying properties similar to those in rat cells. However, a much smaller proportion of bovine cells exhibit inactivating BK current, the proportion of the total current that inactivates is usually smaller, and the rate of inactivation is often much slower. Other gating features differ as well; the voltage dependence of channel activation i...
Calcium- and voltage-activated potassium channels in adrenocortical cell membranes
Biochimica et Biophysica Acta (BBA) - Biomembranes, 1985
Current flowing through single Ca-and voltage-activated K channels has been recorded from cell-attached and inside-out excised membrane patches of cultured Y-I adrenocortical cells, in intact cells, single-channel current amplitude and the time a channel stays in the open state increase with membrane depolarization. In excised patches bathed in symmetrical 130 mM K solutions, single-channel conductance is 170 pS. This value is constant in the membrane potential range of + 50 mV but decreases at larger hyper-and depolarizations. Channel open probability is heavily influenced by the concentration of ionic Ca at the inner surface of the membrane in the range between 0.01 and 10 pM. When internal Ca concentration is close to 0.0| pM, channels are usually closed even at large depolarizing voltages. With larger Ca concentrations, channel open probability increases and its voltage dependence is greater. These channels are uniformly distributed in the plasma membrane, since one to four channels were seen in more than ~ of the patches isolated in this study. There are previous reports suggesting a role for calcium ions in the secretory response of adrenocortical cells to ACTH. Therefore, it is possible that, as in other endocrine cells, these K channels modulate Ca influx across the plasma membrane and thus contribute to regulate steroid biosynthesis and release.
The Journal of Membrane Biology, 1995
We report here the presence of a Ca 2+independent K+-channel of large conductance in adrenal chromaffin cell secretory vesicle membranes which is controlled by inhibitory as well as stimulatory heterotrimeric GTP-binding proteins. Using antibodies against specific o~ subunits for immunoblot analysis, we were able to identify the presence of the inhibitory Gi2 and Gi3 subtypes, as well as the stimulatory G O and G~ subtypes, but not Gil in adrenal chromaffin granules. Furthermore, functional analysis of the K+-channel incorporated into planar lipid bilayers showed that GDP[3S and GTPyS have opposite effects on channel activity inducing interconversions between a low and a high open-probability state. Consistent with these findings, the same antibodies antagonized the effects of the nonhydrolyzable analogues on the open probability of the K+-channel.
Brain Research, 1994
To determine the extent which Ca dependent K current (IKCa) contributes during an action potential (AP), bovine chromaffin cells were voltage-clamped using a pre-recorded AP as the command voltage waveform. Based on (1) differential sensitivity of IKCa and Ca-independent K current (IK) to tetraethylammonium; (2) measurements of AP currents under conditions where Ca activation of IKCa had been abolished; and (3) blockade by charybdotoxin, IKCa comprised 70-90% of the outward K current during AP repolarization. In addition, observations are made concerning the form of AP-evoked Ca current.