The calcium‐activated potassium conductance in guinea‐pig myenteric neurones

Abstract

SUMMARY1. Intracellular recordings were made from guinea-pig myenteric neurones in vitro.2. From one to sixty action potentials were followed by an afterhyperpolarization, the amplitude and duration of which increased with the number of preceding action potentials.3

Morphine augments calcium‐dependent potassium conductance in guinea‐pig myenteric neurones

“…In contrast, doubling the calcium concentration to 5 mM increased the afterhyperpolarization duration (Morita et al, 1982) but reduced or prevented the action of morphine.…”

“…The morphine effect on the action potential and afterhyperpolarization were determined after resetting the potential to its control level by passing a small depolarizing current. OPIATES AND GK,ca 619 (Morita et al, 1982). However, in morphine the decline appeared not to be a single exponential; it included a later slow decay phase which was not obvious in the absence of morphine (Figure 1).…”

“…In several cells, we measured the fractional conductance increase (GK,Ca) during the afterhyperpolarization and found this to be similarly affected by morphine. However, this gives little additional information because when the amplitude of the afterhyperpolarization is small (up to 10 mV), it is almost linearly related to GK,Ca (Morita et al, 1982).…”

“…The resting membrane potential of the 13 cells studied was -61.3 ± 1.4mV (mean ± s.e.). The fractional conductance increase during the afterhyperpolarization (GK,Ca) was calculated because the large amplitude of the afterhyperpolarization results in a significant reduction in driving force for the outward potassium current (Morita et al, 1982).…”

“…This is particularly true in the guinea-pig myenteric plexus AH neurones (Grafe et al, 1980;Morita & North, 1981). These cells have a longlasting afterhyperpolarization following the action potential which results from activation of potassium conductance by calcium entry during the action potential (Hirst & Spence, 1973;North, 1973;Hirst et al, 1974;Morita et al, 1982).…”