Strontium Mechanism Of Action

Simple salts of the element strontium can effectively suppress sensory irritation caused by chemically and biologically unrelated chemical irritants over a pH range of 0.6 to 12. Because strontium acts within seconds after application, it is likely that it is acting directly on the type-C chemical sensors that transmit stinging, burning, and itching. In animal studies, strontium salts have been reported to directly suppress neuronal depolarization [25,26]. In vivo, strontium is a divalent ion with an ionic radius similar to the divalent calcium ion (1.13 A vs. 0.99 A, respectively) [27]. Strontium also resembles calcium's ability to traverse calcium-selective ion channels and trigger neurotransmitter release from nerve endings. In many systems strontium is, however, less potent than calcium and thus can act as an inhibitor of calcium-dependent depolarization [26,28-31]. Strontium may act to block calcium-dependent pathways that lead to neuronal depolarization. Neurons are also known to be sensitive to compounds that alter the electrostatic field surrounding their plasma membrane and ion channels [32]. Because strontium can alter the electrostatic field of ion channels and reduce ion permeation through them [33,34], strontium may suppress irritant-induced depolarization of unmyelinated sensory neurons. Strontium salts may also directly act on non-neuronal cells such as keratinocytes or immunoregulatory inflammatory cells. For example, strontium salts can suppress keratinocyte-derived TNF-a, IL-1a, and IL-6 in in vitro cultures [35].

The fact that strontium can block the rapid intense irritation caused by a 70% (pH = 0.6) glycolic acid chemical peel without causing numbness or other detectable changes in cutaneous sensations suggests that strontium is highly selective in its ability to regulate type-C nociceptors (Fig. 4). In contrast, local anesthetics like lidocaine or procaine not only block irritant sensations, but also block tactile sensations that produce numbness [36]. Recent studies support the concept that strontium is highly selective for only nocicep-tive subsets of sensory neurons because strontium nitrate (20%) applied to normal skin did not alter sensory thresholds for cold sensations, warmth sensations, or pain caused by cold or heat [24].

Burning Strontium Nitrate

Figure 4 Chemical irritants activate unmyelinated type-C nociceptors and trigger their depolarization. Type-C nociceptors then synapse in the dorsal root ganglia (DRG) of the spinal cord and the signal travels to the brain where it is sensed as sting, burn, or itch. If the stimulation is of sufficient magnitude, interneurons in the DRG send a retrograde signal down the same type-C fibers, which triggers the release of inflammatory substances including substance P, neurokinin A, calcitonin gene-related peptide (CGRP), and other mediators. These substances trigger vasodilation, vascular permeability, and activate inflammatory cells, including mast cells that, in turn, release another set of inflammatory mediators, including histamine, which further activate nociceptive sensory signals and inflammation. Strontium reduces the sensitivity of type-C nociceptors to chemical irritants while not affecting the A-delta nerves that transmit the ability to detect pain.

Figure 4 Chemical irritants activate unmyelinated type-C nociceptors and trigger their depolarization. Type-C nociceptors then synapse in the dorsal root ganglia (DRG) of the spinal cord and the signal travels to the brain where it is sensed as sting, burn, or itch. If the stimulation is of sufficient magnitude, interneurons in the DRG send a retrograde signal down the same type-C fibers, which triggers the release of inflammatory substances including substance P, neurokinin A, calcitonin gene-related peptide (CGRP), and other mediators. These substances trigger vasodilation, vascular permeability, and activate inflammatory cells, including mast cells that, in turn, release another set of inflammatory mediators, including histamine, which further activate nociceptive sensory signals and inflammation. Strontium reduces the sensitivity of type-C nociceptors to chemical irritants while not affecting the A-delta nerves that transmit the ability to detect pain.

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Responses

  • frodo
    What is the mode of action of strontium?
    5 months ago

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