cAMP increases junctional conductance and stimulates phosphorylation of the 27-kDa principal gap junction polypeptide.

Abstract

Membrane-permeant cAMP derivatives (dibutyryl-and 8-bromo-cAMP) increase gap-junctional conductance within minutes when applied to voltage-clamped pairs of rat hepatocytes. Glucagon also increases junctional conductances, but the response has a more rapid onset and is more rapidly reversible. The glucagon effect can be prevented by intracellular injection of the protein inhibitor of the cAMPdependent protein kinase (Walsh inhibitor), indicating that the catalytic subunit of cAMP-dependent protein kinase is directly involved. The 27-kDa miijor gap junction polypeptide is phosphorylated when liver cells dissociated into small groups are incubated with 32p. Addition of 8-bromo-cAMP to cells increases the incorporation of 32P into the 27-kDa junctional protein. Serine is the amino acid residue that is phosphorylated. When isolated liver gap junctions are incubated in the presence of catalytic subunit of the cAMP-dependent protein kinase, the 27-kDa gap junction polypeptide is phosphorylated with low stoichiometry on serine. The rapid increases in gap junctional conductance caused by agents that elevate cAMP and phosphorylation of the gap junction protein by cAMPdependent protein kinase suggest that cAMP-dependent phosphorylation of the gap junction channel modulates the conductance of liver gap junctions.

Regulation of gap junctions by protein phosphorylation

“…Cx32 was one of the first channel-forming proteins shown to be phosphorylated in intact cells (63). Activation of either cAMP-dPK or PKC increases the state of phosphorylation of Cx32 (34,63,70,72) and at least the effect of cAMP-dPK is temporally correlated with an increased junctional conductance (g j ).…”

Deficient assembly and function of gap junctions in Trf1, a trafficking mutant of the human liver-derived cell line HuH-7

“…From a functional perspective, several studies of assembly and regulation of gap junctions comprising Cx43 have emphasized apparent correlates with phosphorylation, 7,22,26,28,[41][42][43][44][45][46][47][48][49] although Cx26, which is capable of forming gap junctions, does not appear to be phosphorylated [50][51][52] ; truncation mutants of Cx43, which lack the phosphorylation sites also form functional channels. [53][54][55][56] Formation of the more highly phosphorylated form of Cx43 appears to correlate with plasma membrane insertion and its assembly into gap junctions, 28,43 although such slower migrating forms can arise under other conditions and initial phosphorylation may occur as early as in the Golgi apparatus.…”

Different changes in expression and function of connexin 26 and connexin 32 during DNA synthesis and redifferentiation in primary rat hepatocytes using a DMSO culture system

“…In the present cultures, almost confluent hepatocytes cultured in the medium Gap junctions are intercellular membrane channels that containing EGF with 2% DMSO and 10 07 mol/L glucagon, link neighboring cells and mediate reciprocal exchanges of underwent a nearly synchronous wave of DNA synthesis insmall molecules of less than 1,000 Da and ions, including duced by the removal of 2% DMSO and 10 07 mol/L glucagon, second messengers, such as cyclic adenosine monophosphate and the addition of 10 mmol/L nicotinamide, after which the inositol triphosphate, and Ca 2/ , between adjacent cells in DNA synthesis was completely re-inhibited by the re-addition contact. [1][2][3][4] Gap junctions are composed of proteins termed of 2% DMSO and 10 07 mol/L glucagon. During stimulation of ''connexins (Cxs)''.…”