Differential modulation of Ca2+-activated K+ channels in ovine pituitary gonadotrophs by GnRH, Ca2+ and cyclic AMP

Sikdar, SK; McIntosh, Rosalind P.; Mason, William T.

doi:10.1016/0006-8993(89)91057-3

Cited by 35 publications

(16 citation statements)

References 21 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Although we do not directly demonstrate phosphorylation of the BK channel proteins, they are the likely substrates of protein kinase C. Purified protein kinase C regulates BK channel activity in cell-free patches from coronary smooth muscle (Minami et al 1993) as well as reconstituted rat brain BK channels in lipid bilayers (Rheinhart & Levitan, 1995). BK channels in cell-free patches from pituitary cells are also inhibited by cAMP-dependent protein kinase (Sikdar et al 1989). However, as PdBu had no effect on cAMP metabolism in GHi4C cells under our conditions, the inhibitory effect of PdBu is unlikely to be mediated through protein kinase A.…”

Section: Discussionmentioning

confidence: 62%

Activation of protein kinase C inhibits calcium‐activated potassium channels in rat pituitary tumour cells.

Shipston

Armstrong

1996

The Journal of Physiology

View full text Add to dashboard Cite

1. The regulation of large-conductance, calcium-and voltage-dependent potassium (BK) channels by protein kinase C (PKC) was investigated in clonal rat anterior pituitary cells (GH4C1), which were voltage clamped at -40 mV in a physiological potassium gradient through amphotericin-perforated patches. 2. Maximal activation of PKC by 100 nm phorbol 12,13-dibutyrate (PdBu) almost completely inhibited the voltage-activated outward current through BK channels. In contrast PdBu had no significant effect on the residual outward current after block of BK channels with 2 mm TEA or 30 nm charybdotoxin. In single-channel recordings from cell-attached patches, PdBu reduced the open probability of BK channels more than eightfold with no significant effect on mean open lifetime or unitary conductance. 3. The effects of PdBu on BK channels were not mimicked by the 4a-isomer, which does not activate PKC, and were blocked almost completely by 25 jm chelerythrine, a specific, noncompetitive PKC inhibitor. 4. PdBu had no significant effect on the amplitude of the pharmacologically isolated, high voltage-activated calcium current. 5. Inhibition of BK channel activity by PKC provides the first molecular mechanism linking hormonal activation of phospholipase C to sustained excitability in pituitary cells.

show abstract

Section: Discussionmentioning

confidence: 62%

Activation of protein kinase C inhibits calcium‐activated potassium channels in rat pituitary tumour cells.

Shipston

Armstrong

1996

The Journal of Physiology

View full text Add to dashboard Cite

show abstract

“…These findings demonstrate a specific requirement for MgATP, which indicates a role for protein phosphorylation in the suppression of BK Ca channel opening. In support of this conclusion, the effect of MgATP was prevented when PKA was inhibited by preaddition of 10 M Rp-cAMPS with 1 M wiptide (PKI [5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20][21][22] (Peninsula Labs)).…”

Section: Resultsmentioning

confidence: 92%

“…Similarly, the BK Ca channels in rat pituitary tumor cells (GH 4 C 1 cells) are also inhibited by phosphorylation. In these cells, maximal stimulation of either protein kinase A (PKA) or C (PKC) completely suppresses BK Ca channel activity in the physiological voltage range (17,18); conversely, hormones that inhibit secretion from GH 4 C 1 cells have been shown to stimulate BK Ca channels through protein dephosphorylation (12,19). Thus, the BK Ca channels in GH 4 C 1 cells are regulated in the same way as many other physiologically relevant examples of BK Ca channels in the brain.…”

mentioning

confidence: 99%

Conditional and Unconditional Inhibition of Calcium-activated Potassium Channels by Reversible Protein Phosphorylation

Hall

Armstrong

2000

Journal of Biological Chemistry

View full text Add to dashboard Cite

Large conductance, calcium-activated potassium channels (BK Ca or maxi-K) are important determinants of membrane excitability in many cell types. We used patch clamp techniques to study the biochemical regulation of native BK Ca channel proteins by endogenous Ser/Thr-directed protein kinases and phosphatases in cell-free membrane patches from rat pituitary tumor cells (GH 4 C 1 ). When protein kinase activity was blocked by removing ATP, endogenous protein phosphatases slowly increased BK Ca channel activity approximately 3-fold. Dephosphorylated channels could be activated fully by physiological increases in cytoplasmic calcium or membrane depolarization. In contrast, endogenous protein kinases inhibited BK Ca channel activity at two functionally distinct sites. A closely associated, cAMPdependent protein kinase rapidly reduced channel activity in a conditional manner that could be overcome completely by increasing cytoplasmic free calcium 3-fold or 20 mV further depolarization. Phosphorylation at a pharmacologically distinct site inhibited channel activity unconditionally by reducing availability to approximately half that of maximum at all physiological calcium and voltages. Conditional versus unconditional inhibition of BK Ca channel activity through different protein kinases provides cells with a powerful computational mechanism for regulating membrane excitability.Large conductance, calcium-activated potassium channels (BK Ca or maxi-K channels) are uniquely powerful determinants of electrical activity in the nervous, endocrine, and vascular systems, since they respond directly to both membrane depolarization and calcium accumulation (1). The sensitivity of BK Ca channels to such physiological stimuli can be modified by enzyme pathways mediating reversible phosphorylation of the ion channel proteins or other closely associated regulatory proteins (2). Such reversible protein phosphorylation is the primary mechanism for regulating ion channel activity on the physiological time scale of seconds and minutes (2-4). Modification of the behavior of BK Ca channels has profound effects on the frequency and duration of action potentials in excitable cells, thereby controlling the physiological function of these cells.Electrophysiological measurements indicate that the activity of BK Ca channels in native cells may be up-or down-regulated by reversible protein phosphorylation. For example, protein kinase-induced phosphorylation enhances calcium-activated potassium currents in smooth muscle (5, 6), whereas in photoreceptors (7), hippocampal neurones (8 -11), and neurendocrine cells (12), the currents are inhibited by kinase activity. BK Ca channels exist as multimeric protein complexes composed of two integral membrane subunits, the pore-forming ␣ subunit and the regulatory ␤ subunit (1). All ␣ subunits are apparently coded by the same gene, the slo gene, but alternative RNA splicing during development produces functionally distinct channel proteins in different cell types (13-15). Hence, opposite modulatory effects ...

show abstract

“…Considerable phenotypic diversity in the regulation of native BK Ca channels by PKA-dependent phosphorylation has been reported. In many neurons and smooth muscle cells, PKA activates BK Ca channels (13,16,(27)(28)(29), whereas in endocrine cells of the anterior pituitary, BK Ca channels are inhibited (6,24,30). Whether such physiological diversity results from homo-and͞or heterotetramer assembly of ␣-subunit splice variants in native tissues and͞or involves accessory subunits remains to be determined.…”

Section: Discussionmentioning

confidence: 99%

Distinct stoichiometry of BK _Ca channel tetramer phosphorylation specifies channel activation and inhibition by cAMP-dependent protein kinase

Tian

Coghill

McClafferty

et al. 2004

Proc. Natl. Acad. Sci. U.S.A.

130

View full text Add to dashboard Cite

Large conductance voltage-and calcium-activated potassium (BKCa) channels are important signaling molecules that are regulated by multiple protein kinases and protein phosphatases at multiple sites. The pore-forming ␣-subunits, derived from a single gene that undergoes extensive alternative pre-mRNA splicing, assemble as tetramers. Although consensus phosphorylation sites have been identified within the C-terminal domain of ␣-subunits, it is not known whether phosphorylation of all or single ␣-subunits within the tetramer is required for functional regulation of the channel. Here, we have exploited a strategy to study single-ion channels in which both the ␣-subunit splice-variant composition is defined and the number of consensus phosphorylation sites available within each tetramer is known. We have used this approach to demonstrate that cAMP-dependent protein kinase (PKA) phosphorylation of the conserved C-terminal PKA consensus site (S899) in all four ␣-subunits is required for channel activation. In contrast, inhibition of BK Ca channel activity requires phosphorylation of only a single ␣-subunit at a splice insert (STREX)-specific PKA consensus site (S4 STREX). Thus, distinct modes of BKCa channel regulation by PKA phosphorylation exist: an ''all-or-nothing'' rule for activation and a ''single-subunit'' rule for inhibition. This essentially digital regulation has important implications for the combinatorial and conditional regulation of BK Ca channels by reversible protein phosphorylation.L arge conductance voltage-and calcium-activated potassium (BK Ca ) channels are important regulators of cellular function in the endocrine, nervous, cardiovascular, and immune systems (1-6). BK Ca channels are assembled as tetramers (7, 8) of pore-forming ␣-subunits encoded by a single gene (9) that undergoes extensive alternative splicing (10, 11). Distinct ␣-subunit splice-variant mRNAs may be expressed in the same cell, differentially expressed between tissues, or even neighboring cells (12, 13), and dynamic modification of splice-variant mRNA expression (14, 15) may result in altered BK Ca channel phenotype and cellular regulation (5).Similar to other tetrameric potassium channels BK Ca channels are potently regulated by a variety of serine͞threonine protein kinases (16), including cAMP-dependent protein kinase (PKA) (10,(17)(18)(19)(20). The functional response of BK Ca channels to PKA phosphorylation depends on the splice-variant ␣-subunit composition of the tetramer (10, 19). For example, PKA activates homotetramers of mammalian ZERO splice variants (10,17,19), whereas PKA inhibits homotetramers of STREX variants (10). This differential regulation of BK Ca channels by PKA depends on functional consensus of PKA phosphorylation sites within the C terminus of the ␣-subunit. PKA activation of ZERO variants requires a functional conserved C-terminal PKA site (S899) (10,17,19), whereas PKA inhibition of STREX requires a functional PKA site (S4 STREX ) within the STREX insert (10).However, it is unknown how many ␣-subunits...

show abstract

Differential modulation of Ca2+-activated K+ channels in ovine pituitary gonadotrophs by GnRH, Ca2+ and cyclic AMP

Cited by 35 publications

References 21 publications

Activation of protein kinase C inhibits calcium‐activated potassium channels in rat pituitary tumour cells.

Activation of protein kinase C inhibits calcium‐activated potassium channels in rat pituitary tumour cells.

Conditional and Unconditional Inhibition of Calcium-activated Potassium Channels by Reversible Protein Phosphorylation

Distinct stoichiometry of BK _Ca channel tetramer phosphorylation specifies channel activation and inhibition by cAMP-dependent protein kinase

Contact Info

Product

Resources

About

Differential modulation of Ca2+-activated K+ channels in ovine pituitary gonadotrophs by GnRH, Ca2+ and cyclic AMP

Cited by 35 publications

References 21 publications

Activation of protein kinase C inhibits calcium‐activated potassium channels in rat pituitary tumour cells.

Activation of protein kinase C inhibits calcium‐activated potassium channels in rat pituitary tumour cells.

Conditional and Unconditional Inhibition of Calcium-activated Potassium Channels by Reversible Protein Phosphorylation

Distinct stoichiometry of BK Ca channel tetramer phosphorylation specifies channel activation and inhibition by cAMP-dependent protein kinase

Contact Info

Product

Resources

About

Distinct stoichiometry of BK _Ca channel tetramer phosphorylation specifies channel activation and inhibition by cAMP-dependent protein kinase