Fenamates: a novel class of reversible gap junction blockers

Understanding how cells communicate through gap junctions is central to cellular physiology. Gap junctions allow direct exchange of ions and small molecules between adjacent cells, and their regulation is crucial for tissue function. Prior research has shown that various drugs can modulate gap junctional communication, but few are known to do so reversibly and specifically. The need for precise tools to study intercellular communication remains unmet. This gap motivated the investigation of fenamates as potential blockers of gap junctions. No prior work had resolved whether fenamates could reversibly inhibit Cx43-mediated communication. This paper's contribution lies in demonstrating that fenamates are effective and reversible blockers of gap junctions. Their mechanism of action is distinct from known inhibitors like protein kinase C modulators or cyclooxygenase inhibitors. This study introduces fenamates as a novel class of agents for studying gap junctional communication.

The aim of this study was to evaluate fenamates as potential blockers of Cx43-mediated intercellular communication. Researchers focused on NRK fibroblasts and SKHep1 cells overexpressing Cx43. They sought to determine whether fenamates could reversibly inhibit gap junctional communication. The study aimed to quantify the potency of different fenamates in blocking electrical coupling. They also aimed to assess whether the effects of fenamates involved changes in intracellular calcium, pH, or protein kinase C activity. The motivation stemmed from the need for reliable and reversible tools to study gap junction function. This work builds on prior knowledge of fenamates' pharmacological properties, which suggested potential for modulating cellular communication. The study's design aimed to provide a clear understanding of fenamates' role in blocking gap junctions.

Researchers used two distinct methods to assess gap junctional communication in cultured cells. Single electrode voltage-clamp step response measurements were employed to evaluate electrical coupling in confluent monolayers of NRK fibroblasts and SKHep1 cells. Dye microinjection was used to confirm the effects of fenamates on intercellular communication. The study compared the effects of three fenamates: meclofenamic acid, niflumic acid, and flufenamic acid. Voltage-clamp experiments measured changes in capacitive current transients and junctional conductance before and after fenamate application. Dye-coupling experiments determined the half-maximal concentration of fenamates required to inhibit communication. The study also assessed whether fenamates affected intracellular calcium, pH, or protein kinase C activity. These methods allowed the researchers to evaluate the specificity and reversibility of fenamates' effects on gap junctions.

Fenamates significantly reduced gap junctional communication in NRK fibroblasts and SKHep1 cells overexpressing Cx43. The capacitive current transient changed from a pattern indicating multiple coupled cells to one resembling a single cell in isolation. Junctional conductance dropped from over 140.7 nS to less than 1.4 nS after fenamate treatment. Electrical coupling could be restored to over 51.8 nS following washout of fenamates. Meclofenamic acid was the most potent blocker, followed by niflumic acid and flufenamic acid. The half-maximal concentration for meclofenamic acid was 25 μM, and for flufenamic acid, it was 40 μM. Fenamates did not alter intracellular calcium, pH, or protein kinase C activity. Voltage-clamp measurements in SKHep1 cells confirmed that fenamates are potent blockers of Cx43-mediated communication.

Fenamates are a novel class of reversible blockers of Cx43-mediated gap junctional communication. The study showed that fenamates can inhibit intercellular communication without affecting intracellular calcium, pH, or protein kinase C activity. Meclofenamic acid was the most effective blocker among the tested fenamates. The effects of fenamates were reversible upon washout, indicating their potential for experimental use. The study did not find evidence that fenamates act through cyclooxygenase inhibition or protein kinase C modulation. These findings suggest that fenamates can serve as useful tools for studying the role of Cx43 in biological processes. The authors propose that fenamates may be used in future studies to investigate the functional significance of gap junctions in various tissues. This work provides a foundation for further exploration of fenamates as pharmacological tools.