Human connexin43 gap junction channels. Regulation of unitary conductances by phosphorylation.

Abstract

Connexin43 is the major gap protein in the heart and cardiovascular system. Single channel recordings of human connexin43 gap junction channels exogenously expressed in transfected SKHep1 cells demonstrate two discrete classes of channel events, with unitary conductances of predominantly 60 to 70 and 90 to 100 pS when recorded with an internal solution containing CsCl as the major current-carrying ionic species and at moderate transjunctional voltages (< 60 mV). Human connexin43 expressed in SKHep1 cells displays multiple electrophoretic mobilities (apparent M(r), approximately 41 to 45 kD) when resolved in Western blots. Treatment of connexin43 from these cells with alkaline phosphatase collapses the bands into a single 41-kD species; application of alkaline phosphatase to the cell interior through patch pipettes yields channels that are predominantly of the larger unitary conductance. The smaller 60- to 70-pS unitary conductance values correspond to the most common channel size seen in cultured rat cardiac myocytes; these channels were more frequently observed after treatment with the phosphatase inhibitor okadaic acid, which was shown to increase phosphorylation of human connexin43 in these cells under similar conditions. Exposure to the protein kinase inhibitor staurosporine shifted the proportion of events toward the largest unitary conductance and resulted in decreased phosphorylation of human connexin43 in seryl residues in these cells. Thus, the unitary conductance of human connexin43 gap junction channels covaries with the phosphorylation state of the protein. This change in unitary conductance appears to be a unique effect of phosphorylation on gap junction channels, since it has not been observed for other ion channels that have thus far been evaluated.

Glycogen synthase kinase 3β transfers cytoprotective signaling through connexin 43 onto mitochondrial ATP-sensitive K + channels

“…Unlike most, although not all, reports of sarcolemmal Cx43 (22)(23)(24), in the present experiments, increased mitochondrial Cx43 activity was associated with Cx43 phosphorylation, supporting the notion of differential regulation of Cx43 depending on the localization, as previously suggested in astrocytes (25). Because GSK3β is a multifunctional kinase, widely distributed in many cellular compartments and serving a multitude of cellular functions, some undesired effects may result from unspecific application of GSK3β inhibitors especially over a chronic time frame (18).…”

Connexin 35/36 is phosphorylated at regulatory sites in the retina

“…Phosphorylation could have a direct effect on channel properties of Cx35/36 gap junctions, as has been seen for a number of other connexin channels. For example, Cx43 channels expressed in SkHep1 cells show a reversible shift from a 90-100 pS main state to a 60-70 pS subconductance state with activation of PKC (Moreno et al, 1994;Kwak et al, 1995). These effects are mediated by phosphorylation of Ser368 by PKC (Lampe et al, 2000).…”

Dopaminergic modulation of tracer coupling in a ganglion-amacrine cell network

“…Most gap junctions are closed by phosphorylation, but junctions from some connexin types are instead opened by phosphorylation (e.g., Moreno et al, 1994). There is precedent in the retina for the opening of gap junctions by phosphorylation.…”