Physiology and Biophysics Discipline

Center for Proteomics and Molecular Therapeutics

Structure & function of inward rectifier K channels

Dr. Sackin is a graduate of Brown University (1970, Physics) and received his PhD from Yale University (1978, Biophysics) where he remained as Postdoctoral fellow (1978-1981) before joining the faculty at Cornell University Medical College as Assistant, and then Associate Professor (1981-1997). Dr. Sackin joined the faculty of The Chicago Medical School (Rosalind Franklin University), where he has been full Professor since 1998. Dr. Sackin's research has been continuously funded by Am. Heart and NIH (NIDDK) (1981-2018).

Our laboratory utilizes the electrophysiology techniques of patch and whole-cell voltage clamping to investigate ion channels in non-excitable cells. Work has focused on channels in the proximal tubule and collecting duct of the kidney, with particular emphasis on permeation and gating of inward rectifier K channels (Kir) using both heterologous expression of channels in Xenopus oocytes and direct incorporation of channel protein into liposomes. This channel constitutes a principal pathway for renal K secretion in mammalian cortical collecting tubule and is essential for the body's potassium balance. 

The picture below shows 2 of 4 subunits of the closed-state of the Kir1.1b inward rectifier potassium channel, found in the thick ascending limb, connecting tubule, and cortical collecting duct of the mammalian kidney. The channel protein spans the membrane where the external solution is at the top, and the cytoplasm is at the bottom. It is regulated by cytoplasmic ATP, internal phosphorylation and cytoplasmic pH. The primary gate of the channel is a pH gate, formed by occlusion of the permeation path at the bundle-crossing of inner transmembrane helices. However, another gate also exists at the selectivity filter. This gate is in series with the bundle-crossing gate and behaves like the C-type inactivation gate of voltage gated Kv channels, found throughout the nervous system.

Site-directed mutagenesis of Kir channels in our lab has helped to define the structural basis for a primary ligand gate at the bundle-crossing of inner transmembrane helices as well as a secondary K-dependent gate at the selectivity filter, operating in series with the bundle-crossing gate.

Publications

Sackin H. (2021, May 29) Hypothesis for renin-angiotensin inhibitor mitigation of COVID-19. Med Hypotheses. vol 152:110609. PMCID: PMC8114589

Nanazashvili, M., Sánchez-Rodríguez, J.E., Fosque, B., Bezanilla, F., Sackin, H.  (2017). LRET Determination of Molecular Distances during pH Gating of the Mammalian Inward Rectifier Kir1.1b.  Biophys J. 114: 88-97.

Sackin, H., Nanazashvili, M., and Makino, S. (2015). Direct injection of cell-free Kir1.1 protein into Xenopus oocytes replicates single-channel currents derived from Kir1.1 mRNA. Channels. 9: 196-199.

Frindt, G., Li, H., Sackin, H., Palmer, L. G. (2013). Inhibition of ROMK channels by low extracellular K and oxidative stress.  Am. J. Physiol. 305 (Renal): F208-F215.

Sackin, H., Nanazashvili, M., Li, H., Palmer, L. G., Yang, L. (2012). Residues at the outer mouth of Kir1.1 determine K-dependent gating. Biophysical Journal. 102: 2742-2750

Yang, L., Edvinsson, J., Sackin, H., and Palmer, L. G.. (2012). Ion selectivity and current saturation in inward rectifier K channels. J. Gen. Physiol. 139: 145-157

Sackin, H., Nanazashvili, M., Li, H., Palmer, L.G. and L. Yang. (2011). Modulation of Kir1.1 inactivation by extracellular Ca and Mg. Biophysical Journal. 100:1207-1215.

Sackin H, Nanazashvili, M., Li,H., Palmer L.G. and D.E. Walters. (2010). A conserved arginine near the filter of Kir1.1 controls Rb/K selectivity. Channels. 4: 203-214.

Sackin H, Nanazashvili, M., Li,H., Palmer L.G. and D.E. Walters. (2009). An inter-subunit salt bridge near the selectivity filter stabilizes the active state of Kir1.1. Biophysical Journal. 97: 1058-1066.

Sackin H, et al. (2007). External K Activation of Kir1.1 depends on the pH Gate. Biophysical Journal Vol 93: L14-L16.

Nanazashvili, M., Li,H., Palmer L.G., Walters D.E., and Sackin H. (2007). Moving the pH gate of the Kir1.1 inward rectifier channel. Channels Vol 1: 21 - 28

Zhang, Y., Sackin, H., and L.G. Palmer (2006). Localization of the pH gate in Kir1.1 channels. Biophysical Journal 91:2901-2909.

Sackin, H., Nanazashvili, M., Palmer, L.G., and Hui Li (2006). Role of conserved glycines in pH gating of Kir1.1 (ROMK). Biophysical Journal 90:3582-3589.

 Sackin H, Nanazashvili, M., Palmer L.G., Krambis, M. and D.E. Walters. (2005). Structural locus of the pH gate in the Kir1.1 inward rectifier channel. Biophysical Journal. 88: 2597-2606.

Sackin H, L.G. Palmer, and M. Krambis. (2004). Potassium-dependent slow inactivation of Kir1.1 (ROMK) channels. Biophysical Journal. 86: 2145-2155.

Dahlmann A, Li M, Gao ZH, McGarrigle D, Sackin H, and L. G. Palmer. (2004). Regulation of Kir channels by intracellular pH and extracellular K+: Mechanisms of Coupling J. Gen. Physiol. 123: 441- 454.

Sackin H, Vasilyev S., Palmer, L.G. and M. Krambis. (2003). Permeant cations and blockers modulate pH gating of ROMK channels. Biophysical Journal. 84: 910-921.

Sackin H, et al. (2007). External K Activation of Kir1.1 depends on the pH Gate. Biophysical Journal Vol 93: L14-L16.

Choe, H., Sackin H, and Palmer, L.G. (2001). Gating Properties of Inward-Rectifier Potassium Channels: Effects of Permeant Ions. J. Memb Biol 184: 81-89.

Choe, H., Sackin H, and Palmer, L.G. (2000). Permeation Properties of Inward-Rectifier Potassium Channels and Their Molecular Determinants J. Gen. Physiol. 115: 391-404.

Choe, H., Palmer, L.G. and Sackin H. (1999). Structural determinants of gating in inward rectifier K channels. Biophysical Journal. 76: 1988-2003.

Frindt, G., Zhou, H., Sackin H. and Palmer, L.G. (1998). Dissociation of K channel density and ROMK mRNA in the rat cortical collecting tubule during K adaptation. Am. J. Physiol. 274(Renal) : F525-F531.

Choe, H., Sackin H, and Palmer, L.G. (1998). Permeation and Gating of an Inwardly Rectifying Potassium Channel: Evidence for a variable energy well.. J. Gen. Physiol. 112: 433 - 446.

Choe, H., Zhou, H., Palmer, L.G. and Sackin H.(1997). A conserved cytoplasmic region of ROMK modulates pH sensitivity, conductance, and gating. Am. J. Physiol. 273 (Renal) : F516-F529.