Identification of Ca2+-activated K+ channels in cells of embryonic chick osteoblast cultures

Abstract

Primary cultures of embryonic chick osteoblasts consist of a heterogeneous cell population. Patch clamp measurements were done on 1- to 5-day-old osteoblasts, osteocytes, fibroblastlike cells, and cells that could not be classified on morphologic criteria. The measurements showed the omnipresence of depolarization-activated high-conductance channels in cell-attached patches. The whole-cell experiments showed an outward rectifying conductance activating at positive membrane potentials. Channels underlying the latter conductance were found to be K+ conducting in outside-out membrane patches. The activation potential of the outward rectifying K+ conductance shifted to negative membrane potentials upon increasing the intracellular Ca2+ concentration within the range of 10(-8)-10(-3.2) M. The same happened with the activation potential of the K+ channels found in outside-out patches. Finally, inside-out patch experiments directly demonstrated the dependency of the activation potential of K+ channels on Ca2+ ions. Thus the identity and main characteristics of Ca2(+)-activated K+ channels expressed by the various cell types present in chick osteoblast cultures have now been established. Decreased input resistances were found in cells of cultures more than 2 days old. This is consistent with the establishment of electrical coupling between the cells. Functions in which Ca2(+)-activated K+ channels could play a role are discussed.

A large-conductance (BK) potassium channel subtype affects both growth and mineralization of human osteoblasts

“…These include voltage-gated K ϩ channels of the S4 family with six transmembrane domains (21,22), an inward rectifier (45), ATP-sensitive K ϩ channels (25), and a two-pore domain K ϩ channel (15). Additionally, the Ca 2ϩ -activated K ϩ channels are well represented: small-, intermediate-, and large-conductance Ca 2ϩ -activated K ϩ channels are present (6,13,21,22,25,26,28,31,32,41).…”

Molecular mechanisms, physiological roles, and therapeutic implications of ion fluxes in bone cells: Emphasis on the cation‐Cl− cotransporters

“…F I G U R E 3 Presumed effect of CCC inhibition on membrane potential in bone cells. The basolateral membranes of osteoclasts and osteoblasts are presumed to be more conductive to cations than anions under normal circumstances due to the presence of several types of K + channels including Kir2.1, Kv1.3, IK Ca , SK Ca , BK Ca, and a number of P2X to name a few (Edelman et al, 1986;Gu et al, 2001;Kelly et al, 1992;Ravesloot et al, 1990;Sims et al, 1991;Wilson et al, 2011). The WNK/OSR1-SPAK pathway is known to inhibit the KCCs and stimulate the Na + -dependent CCCs.…”

“…There is evidence to suggest that K + channel activity at the surface of bone cells is an important determinant of membrane conductance (Chow et al, 1984 ; Edelman et al, 1986 ; Gu et al, 2001 ; Kelly et al, 1992 ; Ravesloot et al, 1990 ; Sims et al, 1991 ; Wilson et al, 2011 ). It could thus play the key role of orienting the movement of many ions by the electrogenic transport pathways of both osteoclasts and osteoblasts in response to a change in CCC activity.…”

“…Based on the studies available, the surface of osteocytes appears to harbor a variety of high‐conductance K + channels and ion transport systems that are not present in osteoblasts (Gu et al, 2001 ; Ravesloot et al, 1990 ). Among the CCC family members, NCC is the only one to have been detected in this cell type but has been the object of no characterizations at this location (Dvorak et al, 2007 ).…”

Large-Conductance Calcium-Activated Potassium Channels and Voltage-Dependent Sodium Channels in Human Cementoblasts

“…These K Ca channels are classified into three subfamilies based on their biophysical and pharmacological properties, and molecular substrates: K Ca 1.1, large-conductance or BK channels; K Ca 3.1, intermediate-conductance or IK channels; and K Ca 2.1 to K Ca 2.3, small-conductance or SK channels (Wei et al, 2005). In odontoblasts and osteoblasts, which are hard tissue-forming cells similar to cementoblasts, plasma membrane signal transduction plays an important role in sensory reception (Shibukawa et al, 2015), neural communication (Moreau et al, 1996;Obata et al, 2007;Ma et al, 2013;Shibukawa et al, 2015;Nishiyama et al, 2016;Sato et al, 2018), and hard tissue formation (Ravesloot et al, 1990;Henney et al, 2009;Tsumura et al, 2010Tsumura et al, , 2012Sato et al, 2013;Kimura et al, 2016;Kojima et al, 2017). To date, expression of the following diverse K + channels has been observed in osteoblasts: voltagegated K + channels, inward-rectifier K + channels, ATP-sensitive K + channels, K Ca channels (BK, IK, and SK channels;Henney et al, 2009), and two-pore-domain K + channels (e.g., Kito et al, 2020).…”