[Properties of synaptic currents during non-adrenergic inhibition of the smooth muscle cells of the large intestine in the guinea pig]

Abstract

Inhibitory junctional currents (IJCs) were recorded under voltage clamp conditions in response to brief transmural stimulation of the circular muscle of the guinea pig colon using the double sucrose gap method in the presence of atropine. The time course of IJC decay was approximately exponential 100-150 ms after the peak value. The IJC amplitude depended linearly on the membrane potential with the reversal potential (-70 mV) near the potassium equilibrium potential. The time constant (tau) of the IJC decay depended exponentially on the membrane potential and became e-fold decreased when the membrane was hyperpolarized approximately by 120 mV. Varying the quantal content of IJC caused an increase of tau upon rising the amount or transmitter released and its decrease with the depression of IJC. Application of ATP (10(-3)M) caused a decrease of tau and IJC amplitude, while apamine reduced the amplitude of IJC without any changes in their time course. The results are discussed in terms of a buffered diffusion hypothesis supposing a cooperative action of transmitter released on junctional receptors.