Diverse ionic currents and electrical activity of cultured myenteric neurons from the guinea pig proximal colon

The aim of this study was to perform a patch-clamp analysis of myenteric ne urons from the guinea pig proximal colon. Neurons were enzymatically disper sed, cultured for 2-7 days, and recorded from using whole cell patch clamp. The majority of cells fired phasically, whereas about one-quarter of the n eurons fired in a tonic manner. Neurons were divided into three types based on the currents activated. The majority of tonically firing neurons lacked an A-type current, but generated a large fast transient outward current th at was associated with the rapid repolarizing phase of an action potential. The fast transient outward current was dependent on calcium entry and was blocked by tetraethylammonium. Cells that expressed both an A-type current and a fast transient outward current were mostly phasic. Depolarization of these cells to suprathreshold potentials from less than -60 mV failed to tr igger action potentials, or action potentials were only triggered after a d elay of >50 ms. However, depolarizations from more positive potentials trig gered action potentials with minimal latency. Neurons that expressed neithe r the A-type current or the fast transient outward current were all phasic. Sixteen percent of neurons were similar to AH/type II neurons in that they generated a prolonged afterhyperpolarization following an action potential . The current underlying the prolonged afterhyperpolarization showed weak i nward rectification and had a reversal potential near the potassium equilib rium potential. Thus cultured isolated myenteric neurons of the guinea pig proximal colon retain many of the diverse properties of intact neurons. Thi s preparation is suitable for further biophysical and molecular characteriz ation of channels expressed in colonic myenteric neurons.