The Large Conductance Potassium Channel β-Subunit Can Interact with and Modulate the Functional Properties of a Calcium-activated Chloride Channel, CLCA1

Abstract

We have recently compared the biophysical and pharmacological properties of native Ca 2؉ -activated Cl ؊ currents in murine portal vein with mCLCA1 channels cloned from murine portal vein myocytes (Britton, F. C., Ohya, S., Horowitz, B., and Greenwood, I. A. (2002) J. Physiol. (Lond.) 539, 107-117). These channels shared a similar relative permeability to various anions, but the expressed channel current lacked the marked time dependence of the native current. In addition, the expressed channel showed a lower Ca 2؉ sensitivity than the native channel. As non-pore-forming regulatory ␤-subunits alter the kinetics and increase the Ca 2؉ sensitivity of Ca 2؉ -dependent K ؉ channels (BK channels) we investigated whether co-expression of ␤-subunits with CLCA1 would alter the kinetics/Ca 2؉ sensitivity of mCLCA1. Internal dialysis of human embryonic kidney cells stably expressing CLCA1 with 500 nM Ca 2؉ evoked a significantly larger current when the ␤-subunit KC-NMB1 was co-expressed. In a small number of co-transfected cells marked time dependence to the activation kinetics was observed. Interaction studies using the mammalian two-hybrid technique demonstrated a physical association between CLCA1 and KCNMB1 when coexpressed in human embryonic kidney cells. These data suggest that activation of CLCA1 can be modified by accessory subunits.

Molecular and Functional Analyses of Two New Calcium-activated Chloride Channel Family Members from Mouse Eye and Intestine

“…Co-expression of a large conductance K ϩ channel (BK channel) ␤-subunit with mCLCA1 in HEK293 cells alters the kinetics and Ca 2ϩ sensitivity of the channel, and the two proteins interact in a mammalian two-hybrid system. This is the only published study that has examined potential accessory subunit interactions with a CLCA family member (43).…”

Structure and Function of CLCA Proteins

“…CLCA proteins have also been connected recently to the regulation of mucus production in the asthmatic airway (88, 135), and to ion transport in the airway of cystic fibrosis patients (83, 84). Other roles include CLCA involvement in chloride transport affecting vascular smooth muscle tone and blood pressure, and in retinal functions that are disrupted in Best's vitelliform macular dystrophy (9,73,94,124).…”

Murine mCLCA6 Is an Integral Apical Membrane Protein of Non-goblet Cell Enterocytes and Co-localizes With the Cystic Fibrosis Transmembrane Conductance Regulator

“…The term CLCA had initially been coined due to a novel calciumactivated chloride current observed following heterologous expression of several CLCA proteins in various cell lines, implying a function such as calcium-activated chloride channels. However, several other functions have been proposed and include adhesion molecule function (Abdel-Ghany et al 2003), bicarbonate channel activity (Thevenod et al 2003), modulation of other channel proteins (Greenwood et al 2002;Loewen et al 2002), inhibition of tumor growth by promoting apoptosis , and protease activity (Pawlowski et al 2006). To date, the CLCA gene family comprises 18 members known in eight mammalian species with six murine and four human homologs reported (Cunningham et al 1995;Gandhi et al 1998;Gruber et al 1998a;Gruber and Pauli 1999;Komiya et al 1999;Lee et al 1999;Romio et al 1999;Elble et al 2002;Leverkoehne and Gruber 2002;Evans et al 2004;Anton et al 2005;Al-Jumaily et al 2007).…”