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 neurons from the guinea pig proximal colon. Neurons were enzymatically dispersed, 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 neurons 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 that 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 trigger action potentials, or action potentials were only triggered after a delay of >50 ms. However, depolarizations from more positive potentials triggered action potentials with minimal latency. Neurons that expressed neither 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 inward rectification and had a reversal potential near the potassium equilibrium potential. Thus cultured isolated myenteric neurons of the guinea pig proximal colon retain many of the diverse properties of intact neurons. This preparation is suitable for further biophysical and molecular characterization of channels expressed in colonic myenteric neurons.