Formula C20H30O2 | Molar mass 302.45 g/mol | |
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Isopimaric acid (IPA) is a toxin which acts as a large conductance Ca2+-activated K+ channel (BK channel) opener.
Contents
Chemistry
IPA is one of the members of the resin acid group which is a tricyclic diterpene. It has a condensed three-ring structure, one carboxyl-group and a (conjugated) double bond.
Target
IPA acts on the large-conductance calcium activated K+ channels (BK channels).
Mode of action
BK channels are formed by α subunits and accessory β subunits arranged in tetramers. The α subunit forms the ion conduction pore and the β subunit contributes to channel gating. IPA interaction with the BK channel enhances Ca2+ and / or voltage sensitivity of the α subunit of BK channels without affecting the channel conductance. In this state BK channels can still be inhibited by one of their inhibitors, like charybdotoxin (CTX). Opening of the BK channel leads to an increased K+-efflux which hyperpolarizes the resting membrane potential, reducing the excitability of the cell in which the BK-channel is expressed.
Toxicity
Studies on rainbow trout hepatocytes have shown that IPA increases intracellular calcium release, leading to a disturbance in the calcium homeostasis. This could be important in the possible toxicity of the toxin.
Therapeutic use
This toxin may be of value in the treatment of urinary bladder overactivity, stroke treatment and in problems with the hyperactivity of (vascular) smooth muscle cells.