Small-conductance Ca2+-activated K+ channels in bovine chromaffin cells (original) (raw)
Related papers
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...
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
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.
The Journal of Physiology, 1995
1. The mechanism by which muscarine, ionomycin or caffeine results in suppression of Caand voltage-dependent outward current in rat adrenal chromaffin cells was evaluated using both whole-cell voltage clamp and single channel recording. 2. The whole-cell current activated following the elevation of the cytosolic calcium concentration ([Ca2+]i) by muscarine inactivates with a time course comparable to that of single Ca2+and voltage-dependent potassium (BK) channels. 3. The whole-cell inactivating current is pharmacologically similar to BK current. 4. The voltage dependence of inactivation and rate of recovery from inactivation are qualitatively similar for both whole-cell current and ensemble averages of single BK channels. Furthermore, changes in the rate of whole-cell current inactivation track expected changes in submembrane [Ca2+]. 5. The suppression of outward current can be accounted for solely by inactivation of BK channels and does not depend on the means by which [Ca2+]i is elevated. 6. Muscarinic acetylcholine receptor (mAChR) activation, changes in holding potential (-50 to-20 mV), and step depolarizations of different amplitude and duration were tested for their ability to elevate [Ca2+]i and thereby regulate the availability of BK current for activation. 7. Following muscarine-induced elevation of [Ca2+]i at holding potentials positive to-40 mV, the availability of BK current for activation was typically reduced by more than 50 %. 8. Holding potentials in the range of-50 to-20 mV produced only slight alterations in the availability of BK current for activation. 9. Step depolarizations that cause maximal rates of Ca2+ influx (0 to +10 mV) must exceed 200 ms to reduce the availability of BK current by approximately 50 %. 10. The results show that the muscarine-induced elevation of [Ca2+]i produces a profound reduction in the availability of BK channels for activation at membrane potentials likely to be physiologically meaningful. Although depolarization-induced Ca2P influx can inactivate BK current, we propose that short duration depolarizations that occur during normal electrical activity will not significantly alter BK channel availability. Rat chromaffin cells express two classes of functionally distinct Ca2P-activated K+ currents (Neely & Lingle, 1992a). One current, resulting from small conductance K+ channels (Park, 1994) and therefore termed the SK current, is blocked by either apamin or curare (Neely & Lingle, 1992a; Park, 1994), is relatively voltage independent (Neely & Lingle, 1992a), and appears similar to currents described in a number of other (both neuronal and non-neuronal) cell types (
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.
International journal of developmental neuroscience : the official journal of the International Society for Developmental Neuroscience, 2009
Prior to the development of adrenal innervation, the adrenal medulla is capable of responding to low blood oxygen directly. However, this response is lost once adrenal innervation is established. Previous work by our group has outlined mechanisms involved in this direct hypoxic response and the means by which innervation causes the loss of the direct hypoxic response in the ovine adrenal. The current study further investigates mechanisms which may underlie the developmental loss of the direct hypoxic response by concentrating on two aspects of cell function which regulate catecholamine secretion: the contribution of different types of Ca2+ channels to the total Ca2+ current and the contribution of each Ca2+ channel type to K+ channel activation. We identified that Ca2+ current size at -40 to -10 mV is increased in amplitude in fetal chromaffin cells. This is not due to the increased prevalence or size of T-type Ca2+ currents present at these voltages. The relative contribution of L-...
Properties of calcium and potassium currents of clonal adrenocortical cells
The Journal of General Physiology, 1989
The ionic currents of clonal Y-1 adrenocortical cells were studied using the whole-cell variant of the patch-clamp technique. These cells had two major current components: a large outward current carried by K ions, and a small inward Ca current. The Ca current depended on the activity of two populations of Ca channels, slow (SD) and fast (FD) deactivating, that could be separated by their different closing time constants (at -80 mV, SD, 3.8 ms, and FD, 0.13 ms). These two kinds of channels also differed in (a) activation threshold (SD, approximately -50 mV; FD, approximately -20 mV), (b) half-maximal activation (SD, between -15 and -10 mV; FD between +10 and +15 mV), and (c) inactivation time course (SD, fast; FD, slow). The total amplitude of the Ca current and the proportion of SD and FD channels varied from cell to cell. The amplitude of the K current was strongly dependent on the internal [Ca2+] and was almost abolished when internal [Ca2+] was less than 0.001 microM. The K curr...
pH modulation of large conductance potassium channel from adrenal chromaffin granules
Molecular Membrane Biology, 2004
We report here that large conductance K selective channel in adrenal chromaffin granules is controlled by pH. We measured electrogenic influx of 86 Rb into chromaffin granules prepared from bovine adrenal gland medulla. The 86 Rb influx was inhibited by acidic pH. Purified chromaffin granule membranes were also fused with planar lipid bilayer. A potassium channel with conductance of 4329/9 pS in symmetric 450 mM KCl was observed after reconstitution into lipid bilayer. The channel activity was unaffected by charybdotoxin, a blocker of the Ca 2 -activated K channel of large conductance. It was observed that acidification to pH 6.4 cis side of the membrane lowered the channel open probability and single channel conductance. Whereas only weak influence on the single channel current amplitude and open probability were observed upon lowering of the pH at the trans side. We conclude that a pH-sensitive large conductance potassium channel operates in the chromaffin granule membrane.
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.