Athermal alterations in the structure of the canalicular membrane and ATPase activity induced by thermal levels of microwave radiation.

Abstract

Sprague-Dawley rats (200-250 g) were exposed 30 min/day for 4 days to thermogenic levels (rectal temperature increase of 2.2 degrees C) of microwave radiation [2.45 GHz, 80 mW/cm2, continuous-wave mode (CW)] or to a radiant heat source resulting in an equivalent increase in body temperature of 2.2 degrees C. On the fifth day after the 4 days of exposure to microwave radiation, the animals were sacrificed and their livers removed. The canalicular membranes were isolated and evaluated for adenosinetriphosphatase (ATPase) activity, total fatty acid composition and membrane fluidity characteristics. Mg(++)-ATPase activity (Vmax) decreased by 48.5% in the group exposed to microwave radiation, with no significant change in the group exposed to radiant heat. The decrease in Mg(++)-ATPase was partially compensated by a concomitant increase in Na+/K(+)-ATPase activity (170% increase in Vmax over control) in animals exposed to microwave radiation, while no change occurred in the group exposed to radiant heat. This alteration in ATPase activity in the group exposed to microwave radiation is associated with a large decrease in the ratio of saturated to unsaturated fatty acids. Conversely, the group exposed to radiant heat had an increase in the ratio of saturated to unsaturated fatty acids. The most dramatic changes were found in the levels of arachidonic acid. Finally, the electron paramagnetic resonance (EPR) spin label technique used to measure the fluidity of the canalicular membranes of the animals in the three groups (sham, microwave radiation and radiant heat) indicated that the results were different in the three groups, reflecting the changes found in their fatty acid composition. The physiological response to "equivalent" thermal loads in rats is expressed differently for different types of energy sources. Possible mechanisms producing these divergent thermogenic responses are discussed.

AI evidence extraction

Main findings

Rats exposed to 2.45 GHz microwave radiation at 80 mW/cm2 (CW) producing a 2.2°C rectal temperature increase showed a 48.5% decrease in canalicular membrane Mg(++)-ATPase activity (Vmax) and a 170% increase in Na+/K(+)-ATPase activity (Vmax) versus control; no significant ATPase changes were reported for an equivalent radiant heat exposure. Microwave exposure was associated with a large decrease in the saturated:unsaturated fatty acid ratio (with notable changes in arachidonic acid), while radiant heat increased this ratio; membrane fluidity differed across sham, microwave, and radiant heat groups consistent with fatty acid composition changes.

Outcomes measured

• Canalicular membrane Mg(++)-ATPase activity (Vmax)
• Canalicular membrane Na+/K(+)-ATPase activity (Vmax)
• Total fatty acid composition (including saturated:unsaturated ratio; arachidonic acid levels)
• Canalicular membrane fluidity (EPR spin label technique)

Limitations

• Sample size not reported in abstract
• SAR not reported; exposure described by power density and thermogenic response
• Outcomes are biochemical/biophysical liver membrane measures; clinical relevance not addressed in abstract
• Timing of assessment limited (sacrifice on fifth day after exposure series)

Suggested hubs

• who-icnirp (0.2)
  Animal study comparing microwave vs radiant heat at equivalent thermal load; potentially relevant to thermal vs non-thermal discussion in exposure guidelines.

{
    "study_type": "animal",
    "exposure": {
        "band": "microwave",
        "source": null,
        "frequency_mhz": 2450,
        "sar_wkg": null,
        "duration": "30 min/day for 4 days"
    },
    "population": "Sprague-Dawley rats (200–250 g)",
    "sample_size": null,
    "outcomes": [
        "Canalicular membrane Mg(++)-ATPase activity (Vmax)",
        "Canalicular membrane Na+/K(+)-ATPase activity (Vmax)",
        "Total fatty acid composition (including saturated:unsaturated ratio; arachidonic acid levels)",
        "Canalicular membrane fluidity (EPR spin label technique)"
    ],
    "main_findings": "Rats exposed to 2.45 GHz microwave radiation at 80 mW/cm2 (CW) producing a 2.2°C rectal temperature increase showed a 48.5% decrease in canalicular membrane Mg(++)-ATPase activity (Vmax) and a 170% increase in Na+/K(+)-ATPase activity (Vmax) versus control; no significant ATPase changes were reported for an equivalent radiant heat exposure. Microwave exposure was associated with a large decrease in the saturated:unsaturated fatty acid ratio (with notable changes in arachidonic acid), while radiant heat increased this ratio; membrane fluidity differed across sham, microwave, and radiant heat groups consistent with fatty acid composition changes.",
    "effect_direction": "harm",
    "limitations": [
        "Sample size not reported in abstract",
        "SAR not reported; exposure described by power density and thermogenic response",
        "Outcomes are biochemical/biophysical liver membrane measures; clinical relevance not addressed in abstract",
        "Timing of assessment limited (sacrifice on fifth day after exposure series)"
    ],
    "evidence_strength": "low",
    "confidence": 0.7800000000000000266453525910037569701671600341796875,
    "peer_reviewed_likely": "yes",
    "keywords": [
        "microwave radiation",
        "2.45 GHz",
        "continuous wave",
        "thermogenic exposure",
        "rats",
        "liver",
        "canalicular membrane",
        "ATPase",
        "Mg-ATPase",
        "Na/K-ATPase",
        "fatty acid composition",
        "arachidonic acid",
        "membrane fluidity",
        "EPR"
    ],
    "suggested_hubs": [
        {
            "slug": "who-icnirp",
            "weight": 0.200000000000000011102230246251565404236316680908203125,
            "reason": "Animal study comparing microwave vs radiant heat at equivalent thermal load; potentially relevant to thermal vs non-thermal discussion in exposure guidelines."
        }
    ]
}

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