Low temperature and muscarinic receptor activities

Area of Science:

• Physiology
• Pharmacology
• Gastrointestinal Motility

Background:

• Smooth muscle automaticity is crucial for gastrointestinal function.
• Temperature's role in modulating smooth muscle excitability is not fully understood.
• Muscarinic receptors and calcium channels are key regulators of smooth muscle contraction.

Purpose of the Study:

• To investigate the effect of temperature changes on guinea pig ileum smooth muscle automaticity.
• To elucidate the underlying mechanisms, including the involvement of muscarinic receptors and calcium influx.
• To explore the role of cooling rate in triggering hypothermia-induced automaticity.

Main Methods:

• Isolated guinea pig ileum preparations were subjected to controlled temperature reductions (37°C to 14°C).
• The effects of cooling on muscle automaticity were observed.
• Pharmacological agents, including a muscarinic antagonist (mepenzolate) and calcium channel blockers (verapamil, 8-(N,N-diethylamino)-octyl-3,4,5-trimethoxybenzoate hydrochloride), were used to probe the mechanisms.

Main Results:

• Lowering temperature from 37°C to 22°C, 18°C, and 14°C induced automaticity in the smooth muscle.
• The amplitude of this hypothermia-induced automaticity was directly proportional to the magnitude of the temperature drop.
• Automaticity was not observed when the temperature was increased from a low baseline, suggesting cooling rate is critical. Both muscarinic receptor activity and calcium influx (transmembrane and cytoplasmic) were implicated in the observed automaticity.

Conclusions:

• Rapid cooling, not just low temperature, acts as a trigger for smooth muscle automaticity in the guinea pig ileum.
• This temperature-induced automaticity is mediated by the activation of muscarinic receptors and involves both transmembrane and cytoplasmic calcium influx.
• The study highlights the complex interplay between temperature, cellular signaling, and smooth muscle excitability.