Regional differences in cholinergic regulation of potassium current in feline esophageal circular smooth muscle

Abstract

Potassium channels are important contributors to membrane excitability in smooth muscles. There are regional differences in resting membrane potential and K ϩ -channel density along the length of the feline circular smooth muscle esophagus. The aim of this study was to assess responses of K ϩ -channel currents to cholinergic (ACh) stimulation along the length of the feline circular smooth muscle esophageal body. Perforated patchclamp technique assessed K ϩ -channel responses to ACh stimulation in isolated smooth muscle cells from the circular muscle layer of the esophageal body at 2 (distal)-and 4-cm (proximal) sites above the lower esophageal sphincter. Western immunoblots assessed ion channel and receptor expression. ACh stimulation produced a transient increase in outward current followed by inhibition of spontaneous transient outward currents. These ACh-induced currents were abolished by blockers of large-conductance Ca 2ϩ -dependent K ϩ channels (BKCa). Distal cells demonstrated a greater peak current density in outward current than cells from the proximal region and a longerlasting outward current increase. These responses were abolished by atropine and the specific M3 receptor antagonist 4-DAMP but not the M1 receptor antagonist pirenzipine or the M2 receptor antagonist methoctramine. BKCa expression along the smooth muscle esophagus was similar, but M3 receptor expression was greater in the distal region. Therefore, ACh can differentially activate a potassium channel (BKCa) current along the smooth muscle esophagus. This activation probably occurs through release of intracellular calcium via an M3 pathway and has the potential to modulate the timing and amplitude of peristaltic contraction along the esophagus.

Muscarinic Agonists and Antagonists: Effects on Gastrointestinal Function

“…The pertussis-toxin sensitivity of the response suggests that it is mediated by the G i/o -linked M 2 muscarinic receptor. A similar muscarinic inhibition of K Ca has been demonstrated in colon (Cole et al 1989) and esophagus (Muinuddin et al 2005). Thus, M 2 receptor activation directly inhibits the inhibitory K Ca current that occurs following M 3 receptor activation.…”

Oxygen transport and cell distribution of smooth muscle construct cultured under flow

“…The morphology of the isolated cells exhibited the normal characteristics of typical smooth muscle cells, e.g., dense cytoplasm, oval-shaped nucleolus and hilland-valley pattern upon confluency [112]. However, most of the recent investigations of esophageal smooth muscle cells focused on the cell contraction [202,203], which did not require subculture and proliferation and the subculture capability was rather unknown compared with its counterpart in vascular tissues [112,204]. This information is important because: (1) although vascular smooth muscle cells (VSMCs) in some ways are similar to esophageal smooth muscle cells, there are still many subtle differences such as their respective receptors and ion channels [205] of PESMCs at least 6 times, which was similar to the subculture capability found in vascular SMCs [112] and that at p7, explant cells began dying in significant numbers.…”