Modulation of Kir4.1 and Kir5.1 by hypercapnia and intracellular acidosis

1 CO2 chemoreception may be mediated by the modulation of certain ion channels in neurons. Kir4.1 and Kir5.1, two members of the inward rectifier K+ channel family, are expressed in several brain regions including the brainstem. To test the hypothesis that Kir4.1 and Kir5.1 are modulated by CO2 and pH, we carried out experiments by expressing Kir4.1 and coexpressing Kir4.1 with Kir5.1 (Kir4.1‐Kir5.1) in Xenopus oocytes. K+ currents were then studied using two‐electrode voltage clamp and excised patches. 2 Exposure of the oocytes to CO2 (5, 10 and 15 %) produced a concentration‐dependent inhibition of the whole‐cell K+ currents. This inhibition was fast and reversible. Exposure to 15 % CO2 suppressed Kir4.1 currents by ∼20 % and Kir4.1‐Kir5.1 currents by ∼60 %. 3 The effect of CO2 was likely to be mediated by intracellular acidification, because selective intracellular, but not extracellular, acidification to the measured hypercapnic pH levels lowered the currents as effectively as hypercapnia. 4 In excised inside‐out patches, exposure of the cytosolic side of membranes to solutions with various pH levels brought about a dose‐dependent inhibition of the macroscopic K+ currents. The pK value (‐log of dissociation constant) for the inhibition was 6.03 in the Kir4.1 channels, while it was 7.45 in Kir4.1‐Kir5.1 channels, an increase in pH sensitivity of 1.4 pH units. 5 Hypercapnia without changing pH did not inhibit the Kir4.1 and Kir4.1‐Kir5.1 currents, suggesting that these channels are inhibited by protons rather than molecular CO2. 6 A lysine residue in the N terminus of Kir4.1 is critical. Mutation of this lysine at position 67 to methionine (K67M) completely eliminated the CO2 sensitivity of both the homomeric Kir4.1 and heteromeric Kir4.1‐Kir5.1. 7 These results therefore indicate that the Kir4.1 channel is inhibited during hypercapnia by a decrease in intracellular pH, and the coexpression of Kir4.1 with Kir5.1 greatly enhances channel sensitivity to CO2/pH and may enable cells to detect both increases and decreases in PCO2 and intracellular pH at physiological levels.

[1]  Chun Jiang,et al.  Opposite effects of pH on open‐state probability and single channel conductance of Kir4.1 channels , 1999, The Journal of physiology.

[2]  N. Cui,et al.  Identification of a Critical Motif Responsible for Gating of Kir2.3 Channel by Intracellular Protons* , 1999, The Journal of Biological Chemistry.

[3]  N. Cui,et al.  Effects of intra‐ and extracellular acidifications on single channel Kir2.3 currents , 1999, The Journal of physiology.

[4]  J. Ruppersberg,et al.  Inward rectification in KATP channels: a pH switch in the pore , 1999, The EMBO journal.

[5]  L. Salkoff,et al.  Expression of a functional Kir4 family inward rectifier K+ channel from a gene cloned from mouse liver , 1999, The Journal of physiology.

[6]  P Scheid,et al.  Respiration‐modulated membrane potential and chemosensitivity of locus coeruleus neurones in the in vitro brainstem‐spinal cord of the neonatal rat , 1998, The Journal of physiology.

[7]  G. Giebisch,et al.  pH-dependent modulation of the cloned renal K+ channel, ROMK. , 1998, American journal of physiology. Renal physiology.

[8]  D. Colquhoun,et al.  Binding, gating, affinity and efficacy: The interpretation of structure‐activity relationships for agonists and of the effects of mutating receptors , 1998, British journal of pharmacology.

[9]  G. Richerson,et al.  Chemosensitivity of rat medullary raphe neurones in primary tissue culture , 1998, The Journal of physiology.

[10]  P. Scheid,et al.  Contribution of Ca2+-activated K+ channels to central chemosensitivity in cultivated neurons of fetal rat medulla. , 1998, Journal of neurophysiology.

[11]  D. Hilgemann,et al.  Direct activation of inward rectifier potassium channels by PIP2 and its stabilization by Gβγ , 1998, Nature.

[12]  A. Cupello,et al.  Involvement of phosphatase activities in the run-down of GABAA receptor function in rat cerebellar granule cells in culture , 1998, Neuroscience.

[13]  U. Bonnet,et al.  CO2‐sensitive medullary neurons: activation by intracellular acidification , 1998, Neuroreport.

[14]  H. Choe,et al.  A conserved cytoplasmic region of ROMK modulates pH sensitivity, conductance, and gating. , 1997, American journal of physiology. Renal physiology.

[15]  R. Putnam,et al.  Intracellular pH response to hypercapnia in neurons from chemosensitive areas of the medulla. , 1997, The American journal of physiology.

[16]  G. Aghajanian,et al.  Carbon dioxide regulates the tonic activity of locus coeruleus neurons by modulating a proton- and polyamine-sensitive inward rectifier potassium current , 1997, Neuroscience.

[17]  J. Slightom,et al.  Cloning and Characterization of Two K+ Inward Rectifier (Kir) 1.1 Potassium Channel Homologs from Human Kidney (Kir1.2 and Kir1.3)* , 1997, The Journal of Biological Chemistry.

[18]  L. Jan,et al.  Identification of a titratable lysine residue that determines sensitivity of kidney potassium channels (ROMK) to intracellular pH. , 1996, The EMBO journal.

[19]  J. Ruppersberg,et al.  Extracellular K+ and Intracellular pH Allosterically Regulate Renal Kir1.1 Channels* , 1996, The Journal of Biological Chemistry.

[20]  J. Adelman,et al.  Subunit positional effects revealed by novel heteromeric inwardly rectifying K+ channels. , 1996, The EMBO journal.

[21]  D. Ballantyne,et al.  Chemosensitive medullary neurones in the brainstem‐‐spinal cord preparation of the neonatal rat. , 1996, The Journal of physiology.

[22]  Kathryn L. Coulter,et al.  Identification and molecular localization of a pH-sensing domain for the inward rectifier potassium channel HIR , 1995, Neuron.

[23]  G. Giebisch,et al.  Regulation of ATP-sensitive K+ channel by membrane-bound protein phosphatases in rat principal tubule cell. , 1995, The American journal of physiology.

[24]  S. Snyder,et al.  Cloning and expression of two brain-specific inwardly rectifying potassium channels. , 1995, Proceedings of the National Academy of Sciences of the United States of America.

[25]  K. S. Lee,et al.  Intracellular H+ inhibits a cloned rat kidney outer medulla K+ channel expressed in Xenopus oocytes. , 1995, The American journal of physiology.

[26]  G. Richerson.  Response to CO2 of neurons in the rostral ventral medulla in vitro. , 1995, Journal of neurophysiology.

[27]  F. Sigworth,et al.  Oxygen deprivation activates an ATP-inhibitable K+ channel in substantia nigra neurons , 1994, The Journal of neuroscience : the official journal of the Society for Neuroscience.

[28]  C. Wingo,et al.  Stimulation of total CO2 flux by 10% CO2 in rabbit CCD: role of an apical Sch-28080- and Ba-sensitive mechanism. , 1994, The American journal of physiology.

[29]  M. Kavanaugh,et al.  Cloning and expression of a family of inward rectifier potassium channels. , 1994, Receptors & channels.

[30]  M. Fung,et al.  Responses of respiratory modulated and tonic units in the retrotrapezoid nucleus to CO2. , 1993, Respiration physiology.

[31]  G. Haddad,et al.  Cl‐ and Na+ homeostasis during anoxia in rat hypoglossal neurons: intracellular and extracellular in vitro studies. , 1992, The Journal of physiology.

[32]  D. Bayliss,et al.  Depolarization and stimulation of neurons in nucleus tractus solitarii by carbon dioxide does not require chemical synaptic input , 1990, Neuroscience.

[33]  R. Mitchell,et al.  Neural Regulation of Respiration , 1980, Clinics in chest medicine.

[34]  Loeschcke Hh.  Respiratory adaptations to changes in the acid base status of CSF and brain. , 1973 .

[35]  H. Loeschcke.  Respiratory adaptations to changes in the acid base status of CSF and brain. , 1973, Bulletin de physio-pathologie respiratoire.

[36]  H. Loeschcke,et al.  Ventilatory response to alterations of H+ ion concentration in small areas of the ventral medullary surface. , 1970, Respiration physiology.

[37]  J. Severinghaus,et al.  Respiratory responses mediated through superficial chemosensitive areas on the medulla , 1963, Journal of applied physiology.