Intercellular Ca²⁺signaling in alveolar epithelial cells through gap junctions and by extracellular ATP

Abstract

Inter- and extracellular-mediated changes in intracellular Ca2+ concentration ([Ca2+]i) can ensure coordinated tissue function in the lung. Cultured rat alveolar epithelial cells (AECs) have been shown to respond to secretagogues with increases in [Ca2+]i and have been shown to be gap junctionally coupled. However, communication of [Ca2+]i changes in AECs is not well defined. Monolayers of AECs were mechanically perturbed and monitored for [Ca2+]i changes. Perturbation of AECs was administered by a glass probe to either mechanically stimulate or mechanically wound individual cells. Both approaches induced a change in [Ca2+]i in the stimulated cell that was propagated to neighboring cells (Ca2+ waves). A connexin mimetic peptide shown to uncouple gap junctions eliminated Ca2+ waves in mechanically stimulated cells but had no effect on mechanically wounded cells. In contrast, apyrase, an enzyme that effectively removes ATP from the extracellular milieu, had no effect on mechanically stimulated cells but severely restricted mechanically wounded Ca2+ wave propagation. We conclude that AECs have the ability to communicate coordinated Ca2+ changes using both gap junctions and extracellular ATP.

Connexin 43 mediates spread of Ca2+ -dependent proinflammatory responses in lung capillaries

“…However, the recent availability of the connexin-mimetic peptides gap26 and gap27 provides a suitable alternative to the traditional pharmacological inhibitors (15)(16)(17). These peptides, respectively, bind the sequences VCYDKSFPISHVR and SRPTEKTIFII in extracellular loops 1 and 2 of Cx43 (15,17), blocking gap junctional communication in several cell types (11,15,32). Although the mechanisms are unclear, it is suggested that the peptides inhibit cell communication by either gating or disrupting gap junction channels (11,33,34).…”

“…These peptides, respectively, bind the sequences VCYDKSFPISHVR and SRPTEKTIFII in extracellular loops 1 and 2 of Cx43 (15,17), blocking gap junctional communication in several cell types (11,15,32). Although the mechanisms are unclear, it is suggested that the peptides inhibit cell communication by either gating or disrupting gap junction channels (11,33,34). Attractive features of the gap approach are that the inhibitory effect is reversible and that the mechanistic role of the specific connexin is identified.…”

“…However in contrast to arterioles, systemic capillaries and venules neither express Cx43 nor support gap junctional communication (7). Although it is known that lungs express connexins, including Cx43 (11), the existence and the pathological significance of gap junctional communication among endothelial cells of lung microvessels remain poorly understood.…”

Connexins as therapeutic targets in lung disease

“…Along with the work in [29][30][31][32], this manuscript highlights the role of Cx43 in mediating calcium waves. The paper shows that Cx43-made gap junctions contribute to endothelial cell expression of adhesion molecules for leukocytes.…”

“…Type I epithelial cells, which represent 90% of alveolar cells and are more subjected to mechanical stress, promote the release of surfactants by type II cells through calcium waves propagation via gap junctions ( Figure 2B) [14,29]. It is important to note that transmission of calcium waves from type I to type II cells can also occur via paracrine stimulation of purinergic receptors through ATP release [30,31]. These calcium signals may also help to adjust surfactant production to stimuli such as changes in pulmonary blood pressure [32,33].…”