In vitro microelectrode study of the electrical properties of smooth muscle in equine ileum.

This study using intracellular microelectrode recordings has explored the electrical properties of smooth muscle cells in horse intestines (equine ileum) in vitro. It was observed that fluctuations and spikes in the membrane potential were present irrespective fo the layers of smooth muscle cells, and drugs like nifedipine altered the characteristics of these oscillations but did not stop them.

Study Methodology and Findings

• The researchers utilized intracellular microelectrode recordings, a technique that allows the careful study of electrical properties of cells, on cross-sectional preparations of equine ileum, or horse intestines, superfused in a lab setting.
• In all tested preparations, the scientists observed both membrane potential oscillations and spike potentials, although these recordings were easier to acquire from cells in the longitudinal muscle layer as compared to those in the circular layer.
• The average resting membrane potential (RMP) of smooth muscle cells in the longitudinal muscle layer was found to be about -51.9 mV. The oscillations within this layer held an average amplitude of 4.8 mV and a frequency of 9.0 cycles per minute with each oscillation lasting roughly 5.8 seconds.
• Despite the presence of the toxin ‘tetrodotoxin’, the membrane potential oscillations were preserved, indicating a certain degree of resistance that these cells possess against neurotoxic substances.
• An interesting pattern of waxing and waning i.e., gradually increasing and decreasing, of membrane potential oscillation activity was observed throughout the study.

Role of Nifedipine

• Nifedipine is a medication used for the treatment of high blood pressure and to control angina (chest pain). It works by relaxing the blood vessels.
• In this study, it was observed that nifedipine successfully banished the spiking contractile activity of the smooth muscle. This implies it can relax smooth muscles, consistent with its known pharmacology.
• While nifedipine altered the temporal characteristics or timing of the membrane potential oscillations, it did not stop them. This implies that while nifedipine can interfere with the properties of these oscillations, it is unlikely to completely block their occurrence.