Apical SK potassium channels and Ca2+-dependent anion secretion in endometrial epithelial cells (original) (raw)
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Biophysical Journal, 1998
The Ca 2ϩ sensitivity of large conductance Ca 2ϩ -and voltage-activated K ϩ channels (BK V,Ca ) has been determined in situ in freshly isolated myocytes from the guinea pig urinary bladder. In this study, in situ denotes that BK V,Ca channel activity was recorded without removing the channels from the cell. By combining patch clamp recording in the cell-attached configuration and microfluorometry of fura-2, we were able to correlate BK V,Ca channel activity with changes in cytoplasmic intracellular [Ca 2ϩ ] ([Ca 2ϩ ] i ). The latter were induced by ionomycin, an electroneutral Ca 2ϩ ionophore. At 0 mV, the Hill coefficient (n H ) and the [Ca 2ϩ ] i to attain half of the maximal BK V,Ca channel activity (Ca 50 ) were 8 and 1 M, respectively. The data suggest that this large Hill number was not a consequence of the difference between the nearmembrane [Ca 2ϩ ] ([Ca 2ϩ ] s ) and the bulk [Ca 2ϩ ] i , indicated by fura-2. High Hill numbers in the activation by Ca 2ϩ of BK V,Ca channels have been seen by different groups (e.g., filled squares in of Silberberg, S. D., A. Lagrutta, J. P. Adelman, and K. L. . Biophys. J. 70:2640 -2651. However, such high n H has always been considered a peculiarity rather than the rule. This work shows that a high Ca 2ϩ cooperativity is the normal situation for BK V,Ca channels in myocytes from guinea pig urinary bladder. Furthermore, the Ca 50 did not display any significant variation among different channels or cells. It was also evident that BK V,Ca channel activity could decrease in elevated [Ca 2ϩ ] i , either partially or completely. This work implies that the complete activation of BK V,Ca channels occurs with a smaller increment in [Ca 2ϩ ] s than previously expected from in vitro characterization of the Ca 2ϩ sensitivity of these channels. Additionally, it appears that the activity of BK V,Ca channels in situ does not strictly follow changes in near-membrane [Ca 2ϩ ].
Apical Ca2+-activated potassium channels in mouse parotid acinar cells
The Journal of General Physiology, 2012
Ca(2+) activation of Cl and K channels is a key event underlying stimulated fluid secretion from parotid salivary glands. Cl channels are exclusively present on the apical plasma membrane (PM), whereas the localization of K channels has not been established. Mathematical models have suggested that localization of some K channels to the apical PM is optimum for fluid secretion. A combination of whole cell electrophysiology and temporally resolved digital imaging with local manipulation of intracellular [Ca(2+)] was used to investigate if Ca(2+)-activated K channels are present in the apical PM of parotid acinar cells. Initial experiments established Ca(2+)-buffering conditions that produced brief, localized increases in [Ca(2+)] after focal laser photolysis of caged Ca(2+). Conditions were used to isolate K(+) and Cl(-) conductances. Photolysis at the apical PM resulted in a robust increase in K(+) and Cl(-) currents. A localized reduction in [Ca(2+)] at the apical PM after photolysis of Diazo-2, a caged Ca(2+) chelator, resulted in a decrease in both K(+) and Cl(-) currents. The K(+) currents evoked by apical photolysis were partially blocked by both paxilline and TRAM-34, specific blockers of large-conductance "maxi-K" (BK) and intermediate K (IK), respectively, and almost abolished by incubation with both antagonists. Apical TRAM-34-sensitive K(+) currents were also observed in BK-null parotid acini. In contrast, when the [Ca(2+)] was increased at the basal or lateral PM, no increase in either K(+) or Cl(-) currents was evoked. These data provide strong evidence that K and Cl channels are similarly distributed in the apical PM. Furthermore, both IK and BK channels are present in this domain, and the density of these channels appears higher in the apical versus basolateral PM. Collectively, this study provides support for a model in which fluid secretion is optimized after expression of K channels specifically in the apical PM.
Expression of Potassium Channels in Epithelial Cells Depends on Calcium-activated Cell-Cell Contacts
Harvesting MDCK cells with trypsin-EDTA reduces potassium currents (IK) to a mere 10%, presumably by hydrolysis of K + channels, but replating at con-fluence restores them in 12-18 hr, through a process that requires transcription, translation and exocytic fusion of intracellular membrane vesicles to the plasma membrane (Ponce & Cereijido, 1991; Ponce et al., 1991a). In the present work we find that this restoration of I K also requires cell-cell contacts and the presence of 1.8 rnM Ca 2 § The role of extracellular Ca 2 § may be substituted by 2.0 gM TRH, 10 nM PMA or 200 gg/ml DiC8, drugs that stimulate the system of phospholipase C (PLC) and protein kinase C (PKC). Conversely, the recovery of IK triggered by Ca-dependent contacts can be blocked by 110 gM neomycin, 2.0 gM H7, and 250 nM staurosporine, inhibitors of PLC and PKC. These results suggest that the expression of new K + channels depends on Ca 2 § activated contacts with neighboring cells and that the information is conveyed through PLC and PKC, a process in keeping with changes in its enzymatic activity and cellular distribution of PKC. Plasma membrane is also reduced and restored upon harvesting and replating, and depends on Ca2+-activated contracts. However, the effects of the chemicals tested on I K differ from the ones they elicit on the recovery of plasma membrane, suggesting that cells can independently regulate their population of K + channels and the surface of their membrane.
British Journal of Pharmacology, 1994
1 Contractile responses to KC1 and membrane potentials were determined in aortic rings from spontaneously hypertensive rats (SHR), normotensive Wistar rats (NWR) and Wistar Kyoto rats (WKY) both in the absence and in the presence of the Ca2+-dependent K-channel blockers, apamin and tetraethylammonium (TEA). 2 Compared to NWR, aortic rings from WKY and SHR were less reactive and their Ca2+ uptake after stimulation with K+ was decreased. 3 Smooth muscle cell membrane potentials were higher in aortae from SHR and WKY than in NWR aortae, whereas SHR had higher K+ and lower Na+ intracellular activities than WKY and NWR, suggesting overactivity of the Na+/K+ pump in the hypertensive animals. 4 Treatment with apamin caused depolarization of WKY and SHR aortae, and increased their contractile responses to the same level as those of the NWR. Treatment with TEA also caused depolarization of aortae from WKY and SHR, but in the SHR the depolarization induced by TEA was smaller than that produced by apamin and the contractile responses to KCI did not reach the level of those of aortae from NWR. 5 It is concluded that overactivity of Ca2+-dependent K-channels in aortae of WKY and SHR contributes to their higher membrane potentials and lower responsiveness to vasoconstrictor stimuli. In SHR, an overactive Na+/K+ pump is also present, and the contribution of apamin-sensitive Ca2+dependent K-channels to the membrane potential and reactivity appears to be more relevant than that of TEA-sensitive channels.
Apamin-Sensitive Ca2+-Dependent K+Current and Hyperpolarization in Human Endothelial Cells
Biochemical and Biophysical Research Communications, 1997
current which hyperpolarizes the cell, therefore, accel-Vascular endothelial cells have several types of Ca 2/erates Ca 2/ influx, suggesting that activity of Ca 2/ -dedependent K / current (I K-Ca ). Here, we describe pendent K / channel can regulate production of NO and apamin-sensitive I K-Ca which is activated by treatment related substances (5,6).