Summary
The membrane potential of the cells of the longitudinal muscle of the guinea-pig ileum was recorded intracellularly with glass microelectrodes. Upon changing from isotonic physiological salt solution to sucrose hypertonic solution the spontaneous electrical activity of the membrane was abolished. Spike discharge, but not slow potential changes, was evoked by depolarizing current.
In isotonic or in sucrose hypertonic solution, carbachol or acetylcholine caused spike discharge and produced oscillations of the membrane potential (slow waves) which, in hypertonic solution, were about 20 mV in size and 3 sec in duration.
The effects on the response to carbachol of varying the ionic composition were examined in sucrose-hypertonic solution. Slow waves in response to carbachol were rapidly and reversibly abolished in sodium-deficient solution, though electrical stimulation evoked spikes for considerable periods. Slow waves were abolished also in sodium-free solution. In contrast, carbachol evoked slow waves after 20 min in calcium-free solution (in which the membrane depolarized) if the membrane was electrically repolarized. In chloride-deficient solution a small but significant (p<0.05) increase occurred in the duration of slow waves evoked by carbachol. Carbachol elicited slow waves in potassium-free or in potassium-rich solution. The increases in slow wave size and duration in potassium-free solution fell short of statistical significance (0.1>p>0.05). The depolarization produced by carbachol was significantly (p<0.05) less in sodium-deficient (15 mM) solution but was unaffected by alterations in the external chloride concentrations. In sodium-free solution, carbachol hyperpolarized the membrane. The results support a previous suggestion that the slow waves produced by acetylcholine or carbachol represent an inward sodium current through a slow regenerative ion channel.
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Bolton, T.B. The effects of varying the concentrations of ions in the external solution on the oscillations of the membrane potential (Slow Waves) produced by carbachol in longitudinal ileal muscle. Pflugers Arch. 335, 85–96 (1972). https://doi.org/10.1007/BF00592036
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DOI: https://doi.org/10.1007/BF00592036